I like to use this set, bulky yet stupidly powerful, even more if you set rain (aka peliper with drizzle).
Araquanid @ Chesto Berry
Ability: Water Bubble
EVs: 252 HP / 252 Def / 4 SpD
- Leech Life
Lead with this monster and stockpile into rest, if you can get more than 1 stockpile that is pretty much it for the enemy.
If this is for VGC, pair it up with something that can set up rain, liquidation will pretty much liquidate anything under the rain. (STAB+Water Bubble+Rain)
Checks/Counters in the current meta:
1. Tapu Bulu-Can tank pretty much every hit you have and hammer you to oblivion, unless you have stockpile.
2. Tapu KoKo-Thunderbolt, enough said. Take assault vest or set up a light screen.
Stuff that this thing counters that are popular right now:
The rest of the tapus.
All of the UBs.