Tentacool @ Eviolite
Ability:
Regenerator
EVs: 232 HP / 252 Def / 24 SpD
Bold Nature
- Toxic Spikes
- Rapid Spin
- Scald
- Knock Off/Ice Beam/Sludge Wave
One of the main things stopping Tentacool from being useful is the lack of any kind of recovery. Since spinners come in on hazards as a part of their job, Tentacool finds it difficult to perform its own job well due to the stacking damage of coming on hazards again and again. Regenerator fixes this problem and adds an interesting new and useful spinner to PU.
In practice, Tentacool usually comes in and is able to do 1 action before being forced out by the massive amounts of switch-ins Tentacool has (Poliwrath, Gogoat, Torterra, Piloswine, Pelipper...the list goes on). With this in mind, Regenerator is extremely beneficial to Tentacool since the jellyfish is going to be constantly switching anyway and doesn't have to waste the 1 turn manually healing. Regenerator also heals 33%, which is a little short of the 37.5% that full hazards cause, meaning that Tentacool heals most of the hazard damage off. Anything less than full hazards and Tentacool will spin freely and heal some for the trouble. If only Toxic Spikes are out, then Tentacool can switch in to absorb the hazard without having to spin, do the one action, and then heal for the full 1/3.
As for flavor, some parts of the intricate lifespan of the jellyfish reproduce via budding and fission. Since this is Pokemon, it isn't a large stretch of the imagination to say that Tentacool can use this for healing...or just make a new Tentacool on every switch. No one will notice the difference, I promise.
Having a reliable spinner that isn't weak to rocks and can't be poisoned is something that PU lacks and wants dearly, and Regenerator Tentacool can be just that.