A Quick & Dirty Guide to Homebrewing Legendary Monsters in Dungeons and Dragons 5e
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- Опубликовано: 14 июл 2024
- MONSTERS OF DRAKKENHEIM is 300+ pages of eldritch horror inspired monsters for 5e by the Dungeon Dudes! Coming to Kickstarter March 26th, 2024: www.kickstarter.com/projects/... We break down how to turn any monster in to a legendary monster in 4 easy steps. We also discuss additional possible abilities and Lair Actions to take it to the next level.
TIME STAMPS
0:00 - Intro
1:42 - Applying These Strategies
4:13 - Step 1: Hit Points
5:15 - Step 2: Skills & Saving Throws
7:25 - Step 3: Legendary Resistance
10:17- Step 4: Legendary Actions
17:55 - Optional Steps
21:49 - Lair Actions
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Игры
Looking at the 3.5 versions of the same monster can also help. Because of the bounded accuracy of 5e, the higher level monsters on 5e are of lower power level than their 3.5 counterparts that were considered the same CR. I had my party fight a 3.5 adult blue dragon instead of the 5e version. They had an incredibly tough battle
I remember that demons were quite scary, like the 5E Glabrezu is a bit of a joke compared to the 3.5 version
It took a learning curve to decipher the 3.5 stat blocks but they add amazing variety to a campaign with 5e veterans or dms. Oh a troll has 80 hp? Then why isn’t this one dead? Psyc it’s from 3.5. It also adds variety to say there are 6 barbed devils, 3 of them are 5e and 3 are 3.5 so the fight has 2 distinct monsters built of of the same premise. Or some times 3.5 has stats for stuff not in 5e, like the giant skeleton, my players loved him.
One of the greatest Legendary Actions I've seen is the Lich's ability to roll a d8 and regain a spell slot of that level. I use it for pretty much all my spellcasting bosses (sometimes I'll change it to a d6 or even d4).
That's a Lair Action xd.
@@LoudYapper Your pedantry is rarely appreciated.
for those of you who are tempted to have complicated legendary actions, go for Matt Colville’s Villain Actions. in the video on action oriented monsters, he came up with villain actions as an alternate form of legendary actions: the monster in question has three villain actions and it uses one each round, in a specific order. they still fulfill the same purpose as legendary actions: they make an enemy able to stand up to the party as a notable part of the battle. one of them should do do something cool, one of them should do positioning, and the last one should be big damage.
it’s more work than making a legendary monster because it requires you to come up with abilities that both work and are easy enough to use, something easier said than done. but the flip side is that it’s quite fun to make them! when you do it right, you can tell a little story with what happens round 1, 2, and 3.
I recently replaced a Medusa's snake hair with Beholder Eye-stalks. Petrifying Gaze (not anti-magic) and regular attacks, with a random Beholder eye-stalk on one of three Legendary Actions (or two actions for hurling a statue/previous victim with Telekinesis).
Fun times!
There's another solution to an archmage not having enemies get the drop on him. In fact, one able to cast 9th level spells like that could easily make it happen, and such spells were discussed in other videos. I refer to spells such as Guards and Wards and Alarm. Make some of these spells more permanent, and so when the party fails to spot these magical traps that don't seem to have anything happen when triggered, the archmage knows they're there in his place, where they are in there, and has time to decide if they're enough of a threat to either face themselves or flee.
Foresight also prevents surprise, so It could make for a good pre-buff.
Attack, move, disengage, and a 2pt heal are my go to legendary abilities. I love using lair actions and lair effects to add custom flavor to those encounters.
What I'd do in regards to allowing multiple concentration spells is having the spell be tied to an item.
That would give the players a chance to destroy the item ending the spell or they could steal the item and get to use the spell against them
Imagine grabbing a staff and turning cloud kill against the boss
@@Blandy8521 Nope. If my boss/ players are casting cloud kill with an item, it's with magic beans.
solid idea
I would say that for a big, beefy, juggernaut foe, mobility is more important than just hitting again. The agile foe can dash all over the map on their turn, but for the big ol' bag o' HP to suddenly get away from the barbarian and be next to the sorcerer is much more concerning. "You weren't expecting that, were you? Radogast goes next, and then it is the Souleater's turn"
Was literally talking my brother through this last night! He is a new dm and i have been one for a while (long time fan by the way!) And its doing homebrew. This is one i hope he watches to get more ideas for encounters and bosses
I recently had a sea hag as a final boss for my players and they really enjoyed the encounter. I gave her the night hag start block and switched out her spells to be more thematic to the frozen sea coast environment. Her lair was a cliff face on the edge of the water, surrounded by large rocks. She got 2 legendary actions which were making a claw attack or conjuring a water elemental that took her concentration. The lair actions, were either a 10ft wall of water came through and creatures that failed a strength saving throw would be pushed 20ft towards the cliff face, or until they hit an object which caused them to take 2d6 bludgeoning damage, and they would be knocked prone. The other was strong water currents would pull creatures 20ft into the sea and knock them prone on a failed strength saving throw.
It went really well and my players had a fantastic time!
As someone who is getting ready to have a party of low level characters face their first epic boss battle, but felt the abilities of the appropriate monster(s) were a bit lacking for such a dramatic confrontation, this is EXACTLY what I needed.
This is one of your best DM advice videos.
This information should be in the DMG.
Exactly what I need rn! Perfect for making those tough encounters for my players. Thanks Dungeon Dudes!
This video was even more useful than most of your awesome videos are.
The breakdown of legendary monsters was methodical and well constructed, highlighting some of the most important aspects to implementing them in a very concrete way.
You guys should make a legendary monster checklist based on this video. I wish I had the time to watch it again while taking notes...
Just recently started my first campaign with some friends, and your videos have been a huge help in determining how I built my first character. Thanks for the quality content!
I highly suggest Home Field Advantage Compendium of Lair Actions from the Dungeon Master Guild . This book is a true gem and I.M.H.O a must have in every DM's tool box . There is a whole list of lair actions for every monsters from the MM , VGtM and MtoF .
Also Legendary Bestiary: Legendary Actions for Low-Level Monsters by Christopher Waltz. Provides legendary actions instead of lair actions
Nice ! I'm getting those as soon as possible .🍺
This is such a god send video, that I cannot even describe how much I am thanking you and whatever deity inspired you to make it. I am in a tier 4 game that has gone beyond what 5e was built for, and finally understanding how to make challenging monsters will save both my sanity and the game I'm in. Have already shared the video with my other GM friends.
This video reminded me of Matt Coleville’s action oriented monsters video. Extremely useful if you’re Homebrewing monsters!!
I think matthew colville's action oriented monsters is a simpler solution for creating both the group boss and solo monster.
His monster manual kickstarter, "Flee Mortals!", just started
Indeed. Let's sing their praises zawarudo over!
I love chill touch because it doesn’t chill and it’s not a touch.
I’ve slightly overpowered my characters with some homebrew magic items in my campaign, so this video is very welcome on how to give them challenges without just throwing a dozen monsters at them
Same here. I run a two person party for my little brothers, so they are very op to make up for it.
If legendary resistance is a new thing for your players, you could try visibly telegraphing that to your players. Using the arch mage example, when he expends a use of LR, maybe a gem on his robe or staff goes dim, leaving an amount of gems lit equal to the amount of uses he has left. I wouldn't keep doing that too often, or your players will always look for that, but it could be a way to ease your players into that level of play.
Involving the location is a lot of fun too. Thoroughly enjoyed a recent fight on the shores of the river Styx with a Balor. Whip attack into feeblemind was a compellingly deadly combo for a high level party.
You guys are genuinely life savers constantly! I always enjoy your videos and they are so useful! Keep up the great work!
Excellent guide. I've been thinking on how to do this for the last month. Thank you
That was *very* informative and fun to listen to and I am most definitely wil be trying to apply the guidelines offered here :D Good stuff, Dudes!
I made a special 'demonic' legendary creature for one of my campaigns just a bit ago. One of it's optional attacks was a grapple and one of it's legendary actions vampirically drained the grappled target. Even with only getting half the inflicted damage as HP kept it active quite a long time and it nearly wrecked the party making it one of the biggest and best fights they ever had.
Awesome video! Thanks again Dngeon Dudes.
This is probably my favorite Dungeon Dudes video. and the most useful!
So many ideas for my game running through my head right now!
I’ve been watching this channel as a top go-to-channel for DnD and DM advice for a while now. Great work, guys! Keep it up
Thanks so much!
Great video and perfect timing. I was just ramping up a reoccurring villain into a legendary boss for the finale of tier one. Your Bugbear example is almost exactly what I was looking for. Keep up the great work guys!
Currently home brewing a low level dragon boss for my first ever campaign and this video has helped a lot! Its using a home-brew stat block for the Hellkite from mtg (basically a red dragon wyrmling but its a fully grown monster). Since its going to be the first big bad the party faces I don't want it to TPK them, so I'm planning on having them find it at the entrance of its cave where its recovering from a raid on a small city that left it with a spear in one of its shoulders. This not only slightly lowers its hit points but also cuts its flying speed in half and limits it to only getting 30 feet in the air (well within ranged spells, bows and thrown weapons).
Its also got 2 legendary actions. The first costs 1 action and is called Wing Flap, it forces the players to make a strength save or be knocked prone. The second costs 2 actions and is called Fiery Roar, its basically a much weaker breath attack. Its only a 15 foot cone and deals 1d6 thunder damage + 1d6 fire damage.
This is so incredibly useful, especially when you have a party of 5+ players! Thank you so much for the tips, I had seen them before but here and there, so great to have them fully explained and exemplified in one detailed video
So many great ideas, i have so many ideas for fun boss fights now. Thank you agin for anotherr great video
Almost had a TPK with my last BBEG fight. I messed up by not adjusting the CR for legendary and liar actions.
That said, a 3 legendary action synaptic static really put the fear of the Enchanter in them.
thanks guys amazing video! :D Ive got some new ideas now!
I honestly neay cried when my players wrecked my first bbeg in 1 round. It was really hard. But I'm glad they did because I learned how to take the challenge. And I've learned how to make a more interesting fight.
Great video also I can’t wait to get my Drakkenheim bundle set it’s going to be so fun!!
For double concentration, I would restrict that to a pair of bosses you fight at the same time, because you can split the spells such that not all combinations are available anymore.
Some really good ideas. Thanks 😀
Thank you for this. As a new DM learning how wonky CR is after I've already determined the BBEG, this will be handy.
Agreed! I love blocking exits as a lair action :)
Great video topic! I never use legendary creatures really, so this is helpful.
I had an idea on just taking a plane old Zombie and turning it to a boss, for early tier of play.
My idea was that I basically gave it an aura of 10 feet that the players have to make a constitution saving throw when they enter it for the first time or start there turn in it. If they failed they get poison for a minute.
But now I know how to give it a little bit of a little more of spice.
Edit: Oh I almost forgot. Thanks Dungeon Dudes another helpful video.
Just finally got around to the Zakya Rakshasa that I modified to give legendary actions. It went incredibly well.
I got a lot of great ideas from this video, thanks Dungeon Dudes (tm)!
- The Innkeeper
Y’all make some pretty darn useful videos, but my goodness I’m going to get so much mileage out of this one!!! Sooooo good! Excellent topic. Thank you.
Hey guys. I’m loving your videos on how to do specific monsters. Could you do one for the Yuan-Ti? Specifically an Anathama.
Very useful video, another really could technique I have seen is another TTRPG GM who plays cyberpunk used a very clever method to creating 3 templates for enemy levelling that was using a separate thing for Lawmen. Very useful videos for thinking in the space of home brewing foes.
Good lord putting together my legendary monster was a task, I scoured the sites and even talked about it on the Dungeon Dudes Discord :P, but in the end it balanced well with my party. 10 characters, lvl 13 with top teir gear. Battle took two sessions to finish as they started mid way thru the game and she appeared near the end. Waves upon waves of Yuan-ti beseiging the underwater temple, and her, Venomer Thulsa Se'Sehen (CR 17 Legendary Yuan-ti Anathema) threading her way thru the throng. TCE just came out so both sides were sporting some new spells and when they came up against her Flurry of Bites, they were floored. Compared to the CR 12 version, it was about double HP (350 vs 189) with a 22 AC vs 16, Had Proficiency in STR, CON and WIS. Upping the DC on Ophidiophobia Aura really helped let some of the weenie horde that accompanied her get some shots in and so some early chaos. :) Legendary Actions were Claw attack or Move (1 Action) Cast Spell or Constrict (Costs 2 Actions). Gave her a few more spells but her two top minion's bard spells made copies of her, they thought they were dealing with Mirror Image, but instead they were dealing with two seperate Major Images. If the party got a bead on the right one, the images would weave thru each other like a shell game :)
Guys I’m loving the new content. Felt like you were on vacation for a few weeks. Missed you
One of my favorite legendary monsters was an extremely powerful Dragonlord, some of the most powerful monsters in my world. This lord had become a Dracolich, known as Dracolich Hydazaxyl, and was once a white dragon that underwent the ritual and mastered a burning black fire, that constitutes many of its abilities and its breath weapon.
When it was released from the underdark in my campaign, the party tracked down the Dracolich to his lair, which had been made by him completely stealing the life of everything within a mile of him. They fought him in a gray, desolate forest, and one of his lair actions was where he’d indiscriminately steal the soul of a tiny creature in his lair, and consume it to heal, and any creatures that died would have their souls instantly evaporated, with no way to be brought back to life. It was one of the most memorable encounters I’ve ever run.
I will often give creatures "Legendary Reactions", rather than Legendary Actions. For a PC party of four, they get three reactions, adding reaction abilities like parry, retaliatory attack, reposte, teleport after damage, guard, etc. Rather than giving extra actions that occur between PC turns, the creature will appropriately respond to the PCs actions with their multiple reactions. I limit the number of reactions to one per PC turn.
I’ve made some more complex homebrew legendary monsters based on Renekton and Kindred from League. Turning those video game abilities into DnD abilities is pretty fun!
Wonderful video.
For big, but not boss monsters, I'll add 1 or 2 legendary resistances and a reaction. And if the location is fun, lair actions. Keeps important, but not climactic, battles special.
Another option to multiple concentration spells is to give the enemy the ability to do something like attach the concentration to an object in the room. So instead of just hitting the enemy to force concentration checks the other players can destroy the object, allowing for a more dynamic feel.
Brilliant. I love this.
Wish I had this last year when I started my first campaign lol.
The party snuck up on the first boss and cast hold person. Battle was over before it began 😢 Didn’t even finish the first round lol
Legendary REACTIONS. Give that dragon a mighty roar that can break concentration on all spells, or close its wings to protect itself as a form of counterspell
If you want a dirty trick, have the boss leave the spaces inside the final door with spikes or caltrops. That lowers affected party members movement until they are healed.
This is great! One of the things I have trouble with, especially with spellcasting bosses, is having too many options. This can be exacerbated by adding legendary actions, lair actions, and minions. I generally cut out a bunch of the One Action spells from the monster block that I know I'm never going to use in a 3 or 4 round combat, so that I, as a DM, don't take a long time deciding what the boss is going to do. Does anybody else have other things they do to keep the Boss Battle moving along?
It's always fun to have a simulacrum backing up the archmage. (Double your pleasure, double your fun!)
Generally speaking, having a second and third stage to a battle can also be a fantastic idea. I know if I was a baddy, I'd have something that would preserve my life in case I went down. Potions in particular can dramatically influence the battle, as can magic tattoo and contingencies.
It's really amusing you mentioned the "be careful with having your monster able to concentrate on two spells at once" when just last weekend I ran a session that featured a couple of Phaerimm (Courtesy of Minsc and Boo's journal of villainy), that are able to do just that! It only really came up for one of them (I had 5 in total, my party's a bit of a beast), but either way the party was given a good workout. I wasn't really too worried because they're in a place that would allow them to easily long rest after this, and it was going to be somewhat of a short session for that day anyways, so I figured I might as well make it a bit more deadly. Also, turns out, 8th level magic missile in the dodgy rogue's face because the creatures despise humanoids, is very effective haha. But yes, I totally agree, double concentration should be used sparingly.
Due to factors outside my control, my players will kill a Lich before going to take care of a bunch of goblins... I guess now it's an army of legendary goblins.
The goblins are his phylactery and they all have a sliver of his power now. And you need to kill all of them or else he may come back!😂
Just in time!
An idea I had for a spellcaster thst can concentrate on two spells is that once per day the monster when casting a concentration spell may summon a familiar as part of the concentration, the familiar behaves as normal with the noted exception thst the familiars spirit is the one concentrating on the spell. Due to the image focus this takes it, the familiar is unable to take actions other than disengage or dash. If the familiar is killed or damaged in any way the concentration is broken. This means that the second concentration can be easily broken but for half a round can possibly pull of a nasty combo.
My group has 6 players, so I always fudge HP of monsters closer to max just to give them a fighting chance. Thanks for the amazing advice, I can't wait to use it in my own campaign. Great stuff boys!
The legendary creature I home brewed is entirely stationary. The fight takes place inside a room that is the creature itself, so it can contort and manipulate it to make you have a bad day. Occasionally, an eye will appear in the room. Kill 3 of them, and the heart appears. Being entirely stationary you might believe it’s nothing but a punching bag, but I think a 17AC circumvents this. It can also summon weaker and stronger enemies to distract the party. In addition, any time it kills something, monster or party member, it retains 50hp (maximum of 300). Let me clarify: IT has to KILL them. A monster killed by the party is not eligible. A party member reduced to 0 hit points is not eligible until they have failed all 3 death saves. I believe this would be a good climactic boss for a level 8-10 party. (Yes, it does have legendary resistance, no it cannot cast spells, it is not that smart)
I just upgraded the Medusa for my game and now I'm gonna go over her again with the help of this video to fine tune her. Thank you so much for this video. Any tips on making a Medusa stronger?
I'm in the process of creating a powerful Arch fey who can use a coven of hags as allies. This video will be a big help to finishing that stat block
Quick and dirty legendary and lair actions when I'm in a bind: find a legendary monster of a similar CR and steal them wholesale. Simply alter element type and flavor description as needed.
Idea for the Archmage encounter; the wizard has mage hand. Allow them to release spells from that hand, either touch or ordinary spells.
I would make sure to quite clearly telegraph this ability beforehand, though...
These are all great strategies and I've been using them all before. I would also say that every legendary enemy should also have a decent ranged attack that they can throw out as part of their on-turn action and as a legendary action. If need be, take Eldritch Blast and reskin it.
It’s a crying shame that Medusa’s don’t have regional effects/lair actions.
if you look Hythonia the Cruel is a legendary and Mythic Medusa (CR 17), and she also have lair actions.
She is from the book MOoT :)
A GUIDE TO BUILDING YOUR OWN LEGENDARY MONSTER FROM ONE OF MY PERSONAL FAVORITE CHANNELS??? 😲
I'm in heaven...
this video is super usefull, recently i made a god of death, a CR 30 undead of gargantuar size, its really dangerous but slow and it represents the concept of death itself, it has a flying speed of only 20 feet but its speed cannot be reduced nor its movement stopped, he can cast any spell but only of the necromancy spell list, his only attack consist on automatically kill a creature within range and he has some other features that makes him feel like death itself, something unstopablle, that no matter how much you try, it would come trought your defenses and end you.
It follows.
@@MrRDRII yeah, kinda like it, but bigger, visible to everybody and waaaaay more deadly
So I did an AL one time that said to give the BBEG 4 legendary actions A ROUND!!!! I've had a few parties I've needed to scare a little before the final fight, so I started giving them more legendary actions per combat or round
I'm running a Monster Hunter campaign and my players are about to fight a Tobi-kadachi I've crafted. He has an electrical coating that charges through damage he takes "kinetic energy" which deals damage when he is hit and has a chance to inflict thunderblight once it is charged. He has a repositioning legendary action, one where he shakes on a tree to charge his coat, and a final one thats a sweeping tail attack.
"... and just cribbing the latest strategies that the Dungeon Dudes told you on the internet." I feel personally attacked.
I had a pretty fun boss recounter set up. But the party took a lot of prep time to set up traps and an ambush. They trapped the minions and got the boss with suggestion. I was a little bummed, but they did a great job setting up.
One fun boss 'fight' that I was amused by. The boss of the floor was a gnome wizard. The party successfully got the drop on him. One of the party members realized "Hey this is a gnome, can I tie him in large bag?" Sure why not? Party member succeeds. He then gave the bag with an irate gnome wizard to the Paladin who had Gauntlets of Ogre Strength. I then had to think "What is the damage of the floor?" As they swung the bag repeatedly onto the floor. "But wait, isn't he a caster? He can surely do something right?" Well... Not really. Most spells require line of sight, being in a pillowcase, he couldn't see anything. He was also restrained which means somatic components are significantly harder. Seeing that the gnome was screwed, we ruled that he got knocked unconscious, as the party requested. He got interrogated at the local temple which had several priests/clerics of Kord and Pelor there.
The gnome did not get out alive. We all had fun and it was amusing.
You know this would’ve been so helpful for me last week 🤣
either through my own imbalance creation in items or minor stat block adjustments, my group of 4 12th levels + 1 npc of 12 level was capable of fending off an ancient-ish Red Dragon Draco Lich, Followed by a Black Draco lich in the same initiative combat. The Black Dragon finished off the Red one in a betrayal move, and admittedly, more npcs showed up to heal the party for the new black dragon portion......but ultimately it came down to a successful banishment on the Black Dracolich, followed up with a Critical hit on a bolt of Dragon Slaying the paladin shot upon the dracolich's return. It was an 80+ damage shot. Fun times. Some of their NPC friends failed saves on a curse and died while trying to destroy the phylacteries....but.....oh well.
Something I often do with enemies and a 4+ party is I give out hidden legendary actions to tip the scales more towards balance on the fly. Such as a Vampire Spawn having a "psychic scream" that has the party doing a WIS save or suffer basically the downsides of Tasha's Mind Whip for example.
i like to make the bosses Mythic creatures.
this gives basically 2 phases of a fight where the battle changes, it also does so that the battle is a bit longer. :)
In the past, I turned the Champion monster into a legendary creature. I gave him the attack and dash actions as well. However, I made his 3 Cost Action a sort of inner focus for his next move. Since the monster is a "Champion", I made the ability give the Champion double damage dice until the end of his next turn. This worked well as it meant he could dish out huge damage in one turn, but couldn't crit on other players' turns nor ignore AC. My only mistake was that I gave him a flametongue (meant to be for the barbarian post-fight). I got a crit and realized I accidentally quadrupled the damage due to the ability, downing the warlock from near full hp. This unintentionally scared the other members as I hinted that the Champion was the "weakest" compared to his two brothers.
I had a legendary mage whose legendary action was the ability to quickly requip up to 3 various one off use magic items that he used in place of legendary resistance. (Ie: a ring that would shatter to negate a condition. ) I also considered having thralls who as long as any were chanting could keep focus from being broken.
Loving Kelly’s psychedelic octopus tshirt!! 🐙🐙🐙
monk stunning strike and ranger with ambusher opening usually ridiculous in battles against my monsters
Yep, monk's stun is a nightmare
This is a great video, and I'm relieved I didn't learn anything in it! It's all fantastic info that I've gathered from you guys as well as others (like The Dungeon Coach). My players are always terrified to deal with a boss, and talk about the battle for weeks afterwards
Making your own boss monster that is balanced so as to be challenging and exciting without wiping the group, is a bit daunting for most DM's (myself included). Including 'adds' always felt like a crutch and took away form the boss imo. Thanks so much for this video, it is so very helpful ✌️
Balance... what's that?
Well Chuck Norris doesn't need balance. He basically beats everyone, right?
@@willmena96 lol so true, so true
I once cooked up a shadow-touched shambling mount. Its lair actions were growing and "detonating" mushrooms around the battlefield. Some released damaging acidic spores, some could poison, while others made the players High AF and caused the shambling mount to be under the effect of mirror image
When I ran LMoP and DoIP together, the white dragon was the end boss for the group. I gave him lair actions and a few legendary actions, it really made an epic last battle for the campaign.
This is perfect. I have a Level 4 party that I know are going to steamroll an Ettin miniboss in their next adventure. I don't want him to be completely forgettable. Maybe one legendary resistance and a legendary action or two will toughen him up enough to be challenging.
Lair action for the bug bear
A goblin uses a hidden trap door to make a sneak attack on a creature or knock it prone
Concentration is easy to get around with Glyph of Warding. Ya it self or aoe only but many good buffs fit that. Plus using it as traps thought the battlefield is always great too. Nothing like Sickening Radiance because someone stepped somewhere, which makes the battle more dynamic.
I made my first homebrew legendary for our last session (it was an ancient construct created to defend an also ancient, abandoned library).
Fortunately my PCs negotiated with the construct instead of jumping to combat.
We had extra time and decided to run the combat for fun... they were party wiped in like 3 rounds.
Next time, I'll have the legendary creature balanced a little bit better.
I've found that a party four level 7 characters can take a cr 15 creature with moderate to high difficulty
I've also found that using the mythic rebirth feature can add tension to a final boss fight type of combat
I have a god beefed up Crag Cat.
Dalvakt is master of the storm that encompasses the eastern mountains. He specifically guards the Dreaded Pass, a name given due to his presence. Dozens of hunting parties have had to retreat from combat as he makes the storm worse once within the Dreaded Pass (100ft sight), usually snatching a downed character before making visibility near zero (fight's end). When so close to him, the storms bitter cold is unbearable and cancels any warming effect (Legendary Action (1): Con DC 12, fail 1 damage (more saves as scaling)). He also only attacks via a small breath attack and something similar to the spell Ice Dagger. None know what lies in the lifted peaks behind the pass as Dalvakt is always there to ward off adventurers.
--- This is meant to be a very very hard fight if unprepared, though it will at most only end with one death. Dalvakt was created by (OC) Ixdal, goddess of Nature and Space (distance, not planetary bodies). He was created to protect Skiferren's lair, a legendary Roc that "cleans up" after a game between Ixdal and (OC) Raezma, goddess of Life and Death (They compete to see if civilizations can be nudge to become aberrations or to genocide).
--- Dalvakt has the trickster clerics ability to make a single perfect illusionary doppelganger. With this, he engages parties without ever being in danger. With true sight to see through his blizzard, most are unaware that what they are fighting isn't him. Parties that manage to last 10 turns are hit with a Modify Memory spell and teleported away, those that save getting approached by Ixdal herself to heed warning of bypassing Dalvakt as Skiferren beyond is Reazma's pet and any threat to him in his lair will be met by Reazma herself.
Say the least my players weren't happy, but to be fair I gave them a lot of clues that every fight started and ended the same way. That every former adventurer they talked to stated they retreated for 2 days to regroup, every one said that (It's a long time to retreat, come on!). And there were more clues to be had, and NPC's stated make sure you know what you're going into. One adventurer in the town that leads to the pass got the save and can be pressed into telling given some drink and persuasion/intimidation checks, he's in the Tavern that is even mentioned to be the first stop for getting information.
But he is beatable, he has scaling HP (for encounters with different levels (only 90ish for level 8 party)), and the gods will yield to someone that can. But you do only get one chance if you learn _during_ the fight. That's the challenge part.
Something to up the hit points without having to think about it too much, is to just have their hp be the max amount on all hit dice plus the modifier. Doesn't double the hit points, but may very well be enough.
If I’d let a Legendary creature concentrate on more than one spell at once, they’d need to spend their 3 legendary actions for each round to keep it going…so it would remove a lot of their other capabilities while they do it.
And also, it would still be something that could wreck a party if they aren’t careful.
Late to the party but I haven't seen anyone mention it. If you are using a spellcaster, like the example archmage, that has access to magic missile then be very careful in using it. Each missile is a seperate damage instance, which means it can potentially kill PCs outright.