Since Lopunny's defenses aren't good, you should focus more on her better stats, which are Attack and Speed. So 252 Attack and 252 Speed and 4 in anything else. The nature is also not the best. The best nature for Lopunny is Jolly, which decreases Special Attack and raises Speed, which is good.
Also:
Lopunny (F) @ Lopunnite
Ability: Limber ---> Scrappy
Nature: Jolly (+Spd,-SpA)
EVs: 252 Atk, 252 Spd, 4 HP
-Fake Out
-Return
-Ice Punch
-High Jump Kick
This moveset is only for Mega Lopunny. Fake Out ensures that Lopunny gets the speed boost from the mega evolution safely without getting hurt. Return for Pokemon that resist Ice and Fighting type moves and STAB. Ice Punch to bring down Flying type Pokemon. Lastly, High Jump Kick for STAB and power.