I couldn't think of anything for vanilla Slowbro, but here's one for Mega
Slowbro @ Slowbronite
Ability: Regenerator
EVs: 252 HP / 4 Def / 252 SpA
Quiet nature
- Trick Room
- Surf
- Psychic / Psyshock
- Fire Blast / Ice Beam
Designed as a late game sweeper, while it's weaker than Life Orb Reuniclus it is much bulkier and also has Water STAB. Trick Room turns Slowbro's good awful Speed on its head, letting it outrun everything. Surf is a strong STAB with no drawback. Psychic hits harder, while Psyshock can 2HKO Blissey after some chip damage. Fire Blast hits Grass and Steel types hard while Ice Beam trades hitting Steel types for Dragon types. EVs maximise power and overall bulk.