Stuff Cheeks + Belch Greedent is not viable in Gen 8 ZU
I asked on Smogon, and a user, who is one of the ZU room owners, named S1nn0hC0nfirm3d (aka Ho3nConfirm3d) said:
Greedent has not been viable in ZU for months, and when it was, Stuff Cheeks sets weren't what it ran. Stuff Cheeks is too gimmicky and inconsistent to be pulled off; Greedent is slow and has very limited recovery even when considering Cheek Pouch. It ends up being overwelmed by wallbreakers, and even with offensive sets, it has limited breaking power unless its Belly Drum on Trick Room–needless to say, this set is also very gimmicky and too hard to be pulled off nowadays. Belch isn't worth it because of Greedent's very low Special Attack and Poison coverage doesn't deal with the Ghost-types or physical walls that counter Greedent. Lastly, if you wanted to try defensive boosting sets, there's way better Pokemon like Alcremie, Cofagrigus, and Spiritomb that are way better as defensive sweepers. Again, Greedent is just too slow and vulnerable to pull off any type of setup set, let alone Stuff Cheeks + Belch.
Here are some defensive setup sets for the three Pokemon listed that are better than Stuff Cheeks + Belch Greedent you can try:
Cofagrigus @ Colbur Berry
Ability: Mummy
EVs: 212 HP / 252 Def / 44 Spe
Bold Nature
- Iron Defense
- Body Press
- Shadow Ball
- Rest
Alcremie @ Leftovers
Ability: Aroma Veil
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
- Calm Mind
- Recover
- Dazzling Gleam
- Mystical Fire
or
Alcremie @ Leftovers
Ability: Aroma Veil
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
- Calm Mind
- Acid Armor
- Stored Power
- Rest
Spiritomb @ Leftovers
Ability: Pressure
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Calm Mind
- Dark Pulse
- Rest
- Sleep Talk
tl;dr Greedent is too slow and vulnerable to setup Stuff Cheeks, which is too gimmiky and inconsistent. Belch is also bad on Greedent since Belch is a special move, and Greedent's base special attack is 55. Belch doesn't cover much for Greedent. There are also better defensive setup Pokemon than Greedent.
Hope this helps.
