Azumarill @ Leftovers
Trait : Sap Sipper
Impish Nature (+Def -SpA)
EV's : 252 Atk, 252 Def, 4 SpD.
Defense Curl : To raise your defense and the power of rollout.
Rollout : Increased power each turn, boost from defense curl and EV investment.
Substitute : Only one weakness due to Sap Sipper paired with high defenses. Tough to break.
Focus Punch : Works well with Substitute and boost from EV's.
This Azumarill set is both powerful and defensive. Grass attacks with be converted to a +1 Atk boost too! Hope this helped!