Memento Mori -- Malthael Talents, Overexplained | Heroes of the Storm

Malthael is unintuitive to beginners because he has unique priorities. Your job is to collect XP and kill anything that isn't a Hero. Kill a minion wave, mount up and go to the next, kill that and repeat, on and on. Find time for mercenaries too. This is your default gameplay as Malthael. So much so that you may sometimes sacrifice the first objective for a bigger XP lead in return. Once you unlock Last Rites, you are incentivized to join your team to score a kill with it before you return to your harvesting.
In teamfights, Malthael is a high priority target that so happens to be pretty easy to kill. You have no strong burst damage or CC to speak of. So NEVER jump in first. You jump in only when the fight gets hot and abilities are blown left and right. When you see a clearing where it's safe to teleport in and not get punished, go ahead. Apply your trait to as many Heroes as possible and then... leave the fight. Let the mark burn away their health, and return only when it's time to re-apply it. Do not stand still and brawl. You will die if you linger close to the enemies for a prolonged period of time. Bob and weave, like a mosquito.
That's the essentials that you need to know. Put some practice in and you'll feel more comfortable with his ability usage and how to make it flow.
1:15 - Abilities
11:15 - Level 1
14:53 - Level 4
19:37 - Level 7
24:08 - Level 10
24:20 - Level 13
29:30 - Level 16
33:55 - Level 20
40:00 - My Recommended Talent Builds