Cloyster

Catch a Shellder by fishing in Wild Area (Tested L12, Quirky). Get Water Stone, evolve to Cloyster.
In Poke Centre, relearn Shell Smash, Ice Beam, and Razor Shell. (Get Hydro Pump later on over Icicle Spear, but potentially skip Razor Shell entirely to save a bit of time)

Give Mystic Water to Cloyster.

Fights: SS = Shell Smash, IB = Ice Beam, RS = Razor Shell, HP = Hydro Pump, IS = Icicle Spear.
IB | IB | (Free Heal) | IB, IB

RS, RS, IB | (Free Heal) | X Spec/SS: RS, IB/RS (IB needs good Sp Att)

IB, IB | X Spec/SS (Solosis does 18/27): IB, IB, IB | (Free Heal)

IB | SS: IB, IS (Needs 5, so ideally have Skill Link.) | (Free Heal)
(Go to centre now and relearn Hydro Pump over Icicle Spear)

SS: IB, HP | HP or IB + IB | IB, RS, IB (Can SS to outspeed Corvi+Raboot) | (Free Heal)

SS/X Spec (Was a speed tie in test): HP | SS/X Spec: IB, HP | 2 X Spec, SS: IB, IB, HP | (Free Heal)

HP, SS: IB, IB, IB | RS |
(Heal up if hurt from Bede) SS: IB/(HP if Snarl'd and full) Thievul, IB Liepard, (IB Linoone if alive), IB Pancham | (Free Heal)

SS: IB, IB, IB | (Free Heal)

(Can RS any wilds) | SS: HP/RS, HP/RS, HP (RS on Ninetales/Arcanine if not Burnt)
Note: If poor Sp Att, SS again on Arcanine (it should Agility). You can then RS on Arcanine even if Burnt, and on Centi if not burnt.