598 Ferrothorn

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

Power Whip (90 Power/50 Energy) 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 (100 Power/60 Energy) provides Ferrothorn with an answer to Flying-types meant to counter it. Acid Spray (20 Power/50 Energy) 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.

Ferrothorn is a bulky Grass Pokemon that stands out with its useful Steel sub-typing. Its access to coverage against various Flying-types, in addition to not being weak to most of them and also not being weak to most Water-type coverage attacks, gives Ferrothorn a lot of play in a role that's already heavily contested. While its weakness to Fighting-types makes it difficult to pair with other Steel-type Pokemon, its overall individual performance is not to be underestimated. Just keep this thing away from fire. 

Ferrothorn can operate in the Ultra League by virtue of its resistance list, where it has positive matchup against several bit-names such as Swampert and Venusaur. However, its overall performance is generally too weak to be considered worthwhile out of a few shallow niches.

Durians are noted for having a foul odor, and our Durian friend has that odor on full display in the Master League!