Using its roots as a nervous system, it controls the trees in the forest. It’s kind to the Pokémon that reside in its body.
– Pokémon Y Pokédex
Trevenant was introduced in gen 6. Despite being one of 2 Grass/Ghost families, it’s not version exclusive. It evolves from Phantump via trading, which I discovered by accident (I traded Phantump for Pumpkaboo, and thought they evolved by trading with each other like Shelmet and Karrablast but that’s not the case)
I find Trevenant pretty creepy, perhaps due to my dislike of creepy forests.
Despite it having many weaknesses, Trevenant can be used to stall pretty effectively thanks to its access to Leech Seed and Horn Leech, and its hidden ability of Harvest, which has a 50% chance (or 100% in harsh sunlight) to recycle its held berry. So if given a Sitrus Berry, it can keep healing itself with Leech Seed damage and Sitrus Berry. It has decent defensive stats and good Attack, but is slow (it is a tree after all)