The classy gentlemen of the trio and the only one that’s generally accepted to not suck eggs, Registeel boasts fantastic defenses and phenomenal bulk when combined with his typing. So, what to do? If you want good utility he’s your man but if you want something more try this:
Registeel @ Chesto Berry / Leftovers
Ability: Clear Body
EVs: 252 HP / 4 Def / 252 SpD
- Seismic Toss / Iron Head
- Iron Defense / Curse
With Amnesia even a choice specs Dark Pulse from everyone’s favorite BURASTO BURNO will do pathetically low damage. With Iron Defense, you can laugh at physical attackers all day long. Seismic Toss lets you ignore Registeel’s main weak point - his pathetically low 75/75 offense stats - and just do a flat 100 damage, and with Rest you can fully heal yourself and render all their efforts to little you down moot, as well as remove pesky statuses. It’s practically an impenetrable wall, and it is…but, well, just like actual walls, this set can’t exactly fight back.
If you’d rather not be turned into bait by ooky spooky ghosts, Curse and Iron Head can be used instead to give Registeel respectable power, the inability to be walled completely by anything with a ghost type, and still retain great defensive stats at the cost of slower gains and glacial speed. Of course, a critical hit or sacred sword will cleave right through, but even then it’s possible to recover and even against enemy ghosts you can more often than not PP Stall them to death if you’re that kind of guy. Use Registeel if you want an almost impenetrable wall than can take any hit, and do some decent retaliation.