I decided to revise my Adventure Time team, having tested it on Showdown.
Fionna @ Leftovers
Ability: Huge Power
EVs: 252 HP, 252 Atk, 4 Def
Standard set; I'm not using Choice Band because I found it to be too restricting. I only send Fionna out to use her moves against Pokemon where they will be super effective anyway, so she can KO most things w/o Choice Band.
1 Ice Punch = RIP Garchomp
Cake @ Leftovers
EVs: 252 Def, 128 HP, 128 Sp. Atk
Scizor/ Ferrothorn smasher. Cake doesn't need to fear Scizor or Tyranitar due to being able to outspeed them and burn them. She (it) can also burn physical sweepers so Gumball can take a hit if needed.
I'm so ticked off at Scizor U-Turning and taking 50%+ of her health. :I 1 Flamethrower and Scizor is gone.
BMO @ Eviolite
EVs: 252 HP, 252 Sp. Atk, 4 Def
Why can't BMO learn Flamethrower? Anyway, HP Fire is there to deal with Ferrothorn and Scizor in case I lose Cake. I was thinking of Tri Attack, but HP Fire covers more things.
Marshall Lee @ Choice Scarf
EVs: 252 Atk, 252 Speed, 4 Def
Urgh calm mind stallers... so, Punishment is there to deal with that. Low Kick is really just a filler move, and Foul Play to deal with Swords Dance Pokemon.
Gumball @ Eviolite
Ability: Natural Cure
EVs: 252 Def, 252 HP, 4 Sp. Def
100% susceptible to Taunt, but Gumball is there to Toxic stall. If (s)he's taunted I can just switch out. The reason behind having both Softboiled and Wish on the same set is because Softboiled provides immediate HP recovery for Toxic stalling, and Wish provides team support.
Also I know Chansey are all female, but her design kinda looks like a Gumball so there we go.
Lumpy Space Monarch @ Leftovers
EVs: 252 Def, 252 Sp. Def, 4 Atk
Obligatory hazards clearer. Reflect & Stealth Rock for team support, Earthquake to cover Taunt liability and clear Heatran.