Reserving Perish Trapper (holy shit I thought the above guy reserved it, lucky me)
Primarina @ Chesto Berry / Leftovers / Grip Claw
Ability: Torrent
EVs: 252 HP / 248 Def / 8 SpD
Bold Nature
- Whirlpool
- Perish Song
- Protect
- Rest
Perish Trapper Primarina is easy to describe as there is something with the same defensive typing who also runs this set, Azumarill. This set is slightly bulkier than that one on both sides, however it doesn't have the benefit of Sap Sipper. If you've ever used that set, this one should be pretty self explanatory. Whirlpool on standard Primarina switch-in to trap it (e.g. Toxapex or something like Amoonguss); use Perish Song if successful in trapping said mon. Utilise a mix of Protect and Rest to stall out the 3 Perish Song turns. Then switch on the final turn into something which leaves you in a neutral position once that mon dies.
Primarina does have some cool tools which it can use to differentiate itself from Azumarill further like Encore, Flip Turn (to allow safe switches), Sleep Talk if you want to be funny, Sing if you are a menace to society.
Chesto is the preferred item to allow you to reliably heal up without much penalty from Rest. Leftovers is another decent option if you instead opt to run a cleric on your team. Grip Claw is an interesting choice which lets you trap for 7 turns consistently, allowing you to play around with the extra 2 turns using one of the other potential tools, like Encore more easily. I would more generally recommend this option with other, non perish-variants of whirlpool.
Overall a fun set, which relies heavily on surprise, but can remove a Pex from the game. The hard counter to this set are Gastrodon and Mantine, both of which just laugh at this thing.