Hmm? I thought I'd try this:
Shellos @ Eviolite
Calm | Sticky Hold
252 HP/128 Def/128 SpD
Scald
Toxic
Recover
Stockpile
This little fellow takes hits well after managing to get 3 Stockpile boosts. Scald to burn physical attackers, and is why the nature is more towards the special side. Toxic to stall, and Recover is to recover off damage, and lengthen Shellos' (did I use correct grammar?) life span, making it harder to kill once enough Stockpile boosts are gained. Scald also puts a big bump in the road for non-Guts physical attackers. Some calcs, I guess, for physical attackers:
--252 Atk Haxorus Outrage vs 252 HP/128 +3 Def Eviolite Shellos: 25.56% - 30.34%
--252 Atk Haxorus Outrage + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 12.92% - 15.45%
--252 Atk Life Orb Terrakion Close Combat vs 252 HP/128 +3 Def Eviolite Shellos: 27.81% - 32.87%
--252 Atk Life Orb Terrakion Close Combat + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 14.33% - 16.85%
--252 Atk Life Orb Terrakion Close Combat + Critical Hit vs 252 HP/128 +3 Def Eviolite Shellos: 55.62% - 65.73%
--252 Atk Life Orb Terrakion Close Combat + Critical Hit + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 28.65% - 33.71%
Plus, once Terrakion gets one single defense drop from Close Combat...
0 SpAtk Shellos Scald vs 6 HP/0 -1 SpDef Terrakion: 56.48% - 66.67%
(That looks decent to me.)
Screw him even more with two defense drops!
0 SpAtk Shellos Scald vs 6 HP/0 -2 SpDef Terrakion: 74.07% - 87.96%
(Getting closer...)
And finally, have a chance at a OHKO with, count 'em, three defense drops!
0 SpAtk Shellos Scald vs 6 HP/0 -3 SpDef Terrakion: 93.52% - 110.19%
(58.97% chance to OHKO)
Shellos @ Eviolite
Calm | Sticky Hold
252 HP/128 Def/128 SpD
Scald
Toxic
Recover
Stockpile
This little fellow takes hits well after managing to get 3 Stockpile boosts. Scald to burn physical attackers, and is why the nature is more towards the special side. Toxic to stall, and Recover is to recover off damage, and lengthen Shellos' (did I use correct grammar?) life span, making it harder to kill once enough Stockpile boosts are gained. Scald also puts a big bump in the road for non-Guts physical attackers. Some calcs, I guess, for physical attackers:
--252 Atk Haxorus Outrage vs 252 HP/128 +3 Def Eviolite Shellos: 25.56% - 30.34%
--252 Atk Haxorus Outrage + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 12.92% - 15.45%
--252 Atk Life Orb Terrakion Close Combat vs 252 HP/128 +3 Def Eviolite Shellos: 27.81% - 32.87%
--252 Atk Life Orb Terrakion Close Combat + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 14.33% - 16.85%
--252 Atk Life Orb Terrakion Close Combat + Critical Hit vs 252 HP/128 +3 Def Eviolite Shellos: 55.62% - 65.73%
--252 Atk Life Orb Terrakion Close Combat + Critical Hit + Burn vs 252 HP/128 +3 Def Eviolite Shellos: 28.65% - 33.71%
Plus, once Terrakion gets one single defense drop from Close Combat...
0 SpAtk Shellos Scald vs 6 HP/0 -1 SpDef Terrakion: 56.48% - 66.67%
(That looks decent to me.)
Screw him even more with two defense drops!
0 SpAtk Shellos Scald vs 6 HP/0 -2 SpDef Terrakion: 74.07% - 87.96%
(Getting closer...)
And finally, have a chance at a OHKO with, count 'em, three defense drops!
0 SpAtk Shellos Scald vs 6 HP/0 -3 SpDef Terrakion: 93.52% - 110.19%
(58.97% chance to OHKO)