Trevenant

Trevenant is a Ghost/Grass Pokemon introduced into the game after five years since Pokemon Go first launched in 2016. At this point many players already have strong Ghost and Grass Pokemon for the PvE scene, which makes Trevenant more suitable as a dex filler than a Raid attacker or Gym defender. However its moveset is quite strong in the PvP scene. 

Best PvE Offensive Moveset

• Shadow Claw gets STAB and is the best Fast Move available.
• Sucker Punch provides the same coverage but is a step down for Trevenant.
• Shadow Ball is the strongest Charge Move for Trevenant and pairs well with its Fast Moves.
• Foul Play is a downgrade without STAB.
• Seed Bomb gets STAB but lacks typing synergy. 

Best PvE Defensive Moveset

• Shadow Claw is the better Fast Move for defense due to STAB. 
• Sucker Punch should be TM'd if possible. 
• Seed Bomb performs the best on defense due to its more frequent use as a 3-bar move.
• Foul Play balances a mix of damage output and dodgability.
• Shadow Ball deals the most damage to attackers but also has the slowest damage window. 

Shadow Claw has stronger damage output and faster energy generation than Sucker Punch, and STAB furthers the gap between them even more. 

Seed Bomb is preferred for its lesser energy cost, making it useful for baiting shields, as well as its Grass-type coverage which is backed by STAB. Shadow Ball is a powerful move that hits hard with STAB and is largely unresisted in the overall meta. Foul Play costs a more moderate amount of energy and provides the same coverage as the latter mentioned Charge Move, but the lesser damage output due to lacking STAB discourages its use.