Ferrothorn

Ferrothorn is fairly bulky, but that's about all that can be said for the Thorn Pod Pokemon. Its power is far too low for raids, and its moveset options aren't the best. On the other hand, it's a decent option for defense because of its unique typing and decent moveset. That said; its weakness to Fighting puts it at a disadvantage to one of the gym-cleaning kings, while its double-weakness to Fire can make it little more than a bump in the road.

Best PvE Offensive Moveset

• Bullet Seed pairs with Power Whip to give Ferrothorn its best Grass type moveset.
• Metal Claw pairs with Flash Cannon to make Ferrothorn a Steel type attacker. 
• Acid Spray is worthless on attack.
• Thunder and Mirror Shot give Ferrothorn no advantages on attack.

Best PvE Defensive Moveset

• Bullet Seed and Metal Claw have similar power. However, the former's superior energy gains gives it an edge, while the latter's off-typing with Power Whip makes it viable as well.
• Mirror Shot comes out frequently and has decent power thanks to STAB.
• Power Whip is a good move with STAB and 2-bars, making it a good choice.
• Thunder is hard to dodge and is fairly powerful, though being 1-bar makes it less likely to see use.
• Flash Cannon doesn't offer any appreciable advantages.
• Acid Spray is 3-bar, but far too weak to be worth anything.

Bullet Seed is recommended due to its significantly better energy generation, following the rebalance from April 2020. 

Power Whip is Ferrothorn's bread-and-butter move, sporting good power for reasonable energy cost. Flash Cannon takes advantage of STAB to provide relatively neutral damage, though its coverage typing isn't as valuable. Thunder provides Ferrothorn with an answer to Flying-types meant to counter it. Acid Spray is an objectively weak move, but it has the huge advantage of dropping the opponent's defense by 2 stages, either leaving them highly susceptible to future attacks or forcing a switch, which grants a large tactical advantage to its user.