Yes Trevenant is a fantastic Pokémon to use, with it's Hidden Ability Harvest and a Sitrus Berry to hold it is able to out stall a wide range of Pokémon.
Pokémon with the Ability Harvest, have a 50% chance of restoring a consumed berry each turn. During sunshine this chance increases to 100%. A Sitrus Berry restores 25% of the holders HP when it falls below 50%, so it is basically like infinite recovery unless of course your berry gets eaten, stolen or knocked off. With status moves such as Leech Seed and Will-O-Wisp and STAB physical moves such as Wood Hammer and Shadow Claw, Trevenant isn't a Pokémon that should be taken lightly.
What is a good move set for Trevenant?
Hope I helped :)