Personally, I prefer the air; Aarantula

Huff N. Puff (10 HP, 15 FP, 6 BP) = Level 4
(No screen-wide attacks, EVERYONE must taste death)
Badges: Mega Rush, Dodge Master, Power Bounce, Last Stand
Item: Life Shroom
T1a: Fan Smack (52), Jump (46)
T1b: Tuff Rush, Suck (Heal 11 HP, 57)
HP: 8, FP: 10
T2a: Fan Smack (49), Jump (43)
T2b: Tuff Rush, Blow
HP: 3, FP: 5
T3a: Jump (37), Smack (31)
T3b: Tuff Rush, Suck (Heal 11 HP, 42)
HP: 1, FP: 5
T4a: Power Bounce (Merlee, 8), Outta Sight
T4b: Tuff Rush (Fail), Electrify
HP: 1, FP: 0
T5: Reappear, Jump (1, Death, Life Shroom), Smack (KO)
Fan Smack if the bar is full spawns 5 big Tuff Puffs as opposed to 8 small ones. Since Huff N. Puff will suck all onscreen Tuff Puff down to heal himself, I had to max out his number of Tuff Puffs (10) so that more would spawn than he'd be able to hold.
Originally, this was going to be a fight where my only badge would be Last Stand, but then I realized my level could be made lower by using more badges as it saved me both HP and FP. Didn't want to use Merlee at first either before realizing that she was my best shot at getting enough damage by turn 5 and that Power Bounce would be equally vital. Not to mention being able to save lots on FP as I'd use Fan Smack only for its utility and not for damage like prior versions of this fight did. The FP would have looked uneven though so I found a way to integrate Bow's Outta Sight so the 2 leftover FP wouldn't go to waste while also not being suboptimal (from what I could tell).
I had only the one Life Shroom as an item, too. If mashing was too much of an issue, dropping Last Stand and equipping an HP Plus would make this easier at the expense of another level up.