Shadow Ferrothorn

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.