If you have Cosmic Power for Baton Passing, why doesn't Lopunny have Baton Pass?
Shouldn't that be your fourth move?
But seriously, Encore and Cosmic Power won't necessarily work on Lopunny, unless if you can get into a position that you can set up. (Most people switch out of Encore, so it isn't always good for setting up more than 1 cosmic power, 2 if your faster)
For example, look how much damage Lucario does:
(Lopunny is faster and can use cosmic power before Lucario)
If Lucario attacks first turn:
252 Atk Life Orb Lucario Close Combat vs. +1 0 HP / 0 Def Lopunny: 351-416 (109.3 - 129.5%) -- guaranteed OHKO
(even after boost)
If Lucario is switched in:
252 Atk Life Orb Lucario Close Combat vs. +2 0 HP / 0 Def Lopunny: 265-312 (82.5 - 97.1%) -- guaranteed 2HKO
+ (next Lucario extreme speed so it attacks before def boost to guarantee a KO)
252 Atk Life Orb Lucario Extreme Speed vs. +2 0 HP / 0 Def Lopunny: 58-70 (18 - 21.8%) -- possible 5HKO
And even if it had more boosts, Lucario would set up swords dance. :P
However, If you want an offensive set, Power-Up-Punch and Fake Out are good.
Hope I helped!
Damage Calculating Source