Maybe we can consider an AV Bro, i know that is a bit gimmick but he's so bulky on the special side and a very good movepool, allowing him to hit a lot of defensive threats:
Slowbro @ Assault Vest
Ability: Regenerator
EVs: 248 HP / 252 SpA / 8 SpD
Modest Nature
- Fire Blast
- Scald
- Ice Beam
- Psyshock
Max Special Attack with positive nature is necessary to OHKO 168 SDef Ferrothorn after sr:
252+ SpA Slowbro Fire Blast vs. 252 HP / 168 SpD Ferrothorn: 336-396 (95.4 - 112.5%) -- guaranteed OHKO after Stealth Rock
As i mentioned, his special bulk with the AV is relevand, allowing him to resist two DMeteor from LO tios and a TBolt from LO Thundurus, OHKOing him after the LO damage: 252+ SpA Mega Slowbro Ice Beam vs. 0 HP / 0 SpD Thundurus: 260-306 (86.9 - 102.3%) -- guaranteed OHKO after Stealth Rock
Try him and give me an opinion^^