Originally Posted by Fat Pwnemon
Why would you ever use Registeel instead of Ferrothorn?
1. Registeel is bulkier, especially on the special side where it will be taking Contrary boosted Draco Meteors, Psycho Boosts, and Stored Power. 80 / 150 / 150 blows 74 / 131 / 116 out of the water.
2. Registeel can actually benefit from Heart Swapped Speed boosts. +2 Registeel hits 398 Spe, enough to outrun everything but Deoxys formes. Iron Head's 30% flinch thus becomes an infuriating game changer. Ferrothorn's +2 is a laughable 278, remember the ability isn't Prankster, so there's no priority on it.
Yeah, it's cool that Flash Fire Ferrothorn takes Groudon Nature Power EQ better and turns its 4x Fire weakness into an immunity. Unfortunately it doesn't have the bulk to do what it needs to do, and can't fully capitalize on Heart Swapped speed boosts.