Trevenant's greatest merit, in my opinion, is his ability to
persistently counter the most common Rapid Spinners. (Although, with the latest changes to Defog, that may or may not prove to be worth anything.) As far as his stats go, he doesn't have the greatest bulk, but thanks to his ability options, excellent defensive typing, and great movepool, he's able to utilize an offense stall set to considerable efficiency.
Trevenant @ Sitrus Berry
Ability: Harvest
EVs: 252 HP / 129 DEF / 129 SP. DEF
Nature: Careful
- Horn Leech
- Earthquake
- Leech Seed / Will-O-Wisp / Toxic
- Protect
Shadow Claw and any other sort of Ghost-type coverage was left out mostly due to its irrelevance. The only Rapid Spin users who take super-effective damage from Ghost-type moves are Starmie and Claydol, both of which are already hit super-effectively by Horn Leech (also being 5 BP higher than Shadow Claw as well as its useful regenerative effects). Earthquake not only has better coverage--adding pressure to the likes of Tentacruel, Excadrill, and Torkoal--but is only a measly 5 damage less than STAB Shadow Claw.
The third moveslot is dedicated to residual damage and, in the case of the former two, defensive utility. Which to choose out of Leech Seed, Will-O-Wisp, and Toxic should largely depend on what your team already checks and counters, knowing that Grass, Fire, and Poison-types will negate the effects of each, respectively. Leech Seed would be the preferable option, since it more directly aids Trevenant in his stall approach, while also giving the opportunity to aid other party members upon switch-in.
Protect will maximize the use of Harvest outside of intense sunlight (providing another 50% chance to harvest the Sitrus Berry) while also complimenting the use of either Leech Seed, Will-O-Wisp, or Toxic. It's only because this set utilizes both Harvest and damage-over-time tactics that Protect has a place here. Of course, Protect also has its traditional uses, such as to scout, but that's of lesser importance.
Here are some other unorganized thoughts for consideration:
- Forest's Curse is utter junk. Gourgeist got the better gimmick in Trick-or-Treat, as that at least boosts his STAB Ghost-type moves, whereas Forest's Curse gives the opponent a resistance to Trevenant's most viable STAB moves.
- Trevenant absolutely cannot afford a wasted turn. Because of that, I'm a bit more weary of using Will-O-Wisp over other selections. (I'm aware the accuracy was raised to 85%.)
- Status ailments will ruin most of his viable sets. I'd consider putting a cleric on a team with him, if you aren't instead running a Natural Cure set.
- Assault Vest has no place on Trevenant; he needs his status moves to stay relevant.
- Best shiny in the game.