BIG BOZO

Dondozo will probably have those 6 moves at its disposal. I really hate curse (remember the horror that was 7-Star Meganium), so I was about to slap on Haze, but then I thought of... Another idea... >:)

Bellossom: We Love Her
She's your Dancing Queen and your BIG DAMAGE. Grass Knot is 120 effective power vs BIG BOZO, so it's literally a Solarbeam without needing the Sun or 2 turns. Grass Knot until you can Tera, then use either Growth (if the sun is up) or Quiver Dance (if it isn't) twice, before resuming Grass Knots. Giga Drain is your healing move.

Malamar: The Epic Troll (TM)
The idea that started it all was the ability: Contrary. Flips all stat increases into decreases and vice-versa. So, turn 1 immediately use Skill Swap, giving BIG BOZO Contrary and stealing Unaware (or Water Veil I guess). Meaning when BIG BOZO uses curse, it's weakening itself! Idiot! Psychic Noise is there to prevent healing, but isn't that important. Acupressure is the other funny move here, and we're going to spam it on Bellossom and Slowbro for maximum effect. Psych Up is there if you get bored, it will copy the stat changes of the target (meaning we can copy the boosts from Growth/Quiver Dance/Acupressure/Iron Defense). Tera not required here, but go with Water for the defensive purposes.

Slowbro: He's not really paying attention with that Clear Amulet.
He's here to Scald 3 times, Tera+Iron Defense, Psych Up (On Bellossom), and spam Stored Power. No Shell Bell here folks!

Meganium: Rocky Helmet to keep you safe!
The other silly support. Turn 1, Leech Seed to give yourself some healing (if you miss, don't bother trying again if the shield is up). If you're worried about missing, go with Reflect instead. Follow it up with Sunny Day to increase Growth's potential. Use it again if BIG BOZO uses Rain Dance. Heal Pulse the homies when they're low (Malamar and Slowbro), and Giga Drain when you're low on HP or have nothing else to do. Tera Grass whenever you're able.

https://pokepast.es/521a66fe03d823e5