Lopunny @ None (Klutz) or Charcoal or Big Root (Cute Charm) or Lopunnite ( this moveset isn't designed for a mega Lopunny though)
Trait: Klutz or Cute Charm
(1) 252 Attack, 252 Speed, 6 Sp. Defense
(2) 252 Sp. Defense, 252 attack, 6 Speed
(3) 252 Sp. Defense, 252 Speed, 6 attack
Bounce or Entertainment: Bounce will cover for Fighting weakness. Entertainment can give the users ability to the opponent. Use Entertainment only when Lopunny has Klutz, otherwise, that would be an upgrade for the opponent. Entertainment is not available in generation 4, so in gen. 4, use Bounce.
Hi Jump-Kick: Powerful move, and is STAB if mega evolved. Learned at a low level.
Fire Punch: A powerful move and is learned by Breeding. ( Field and Human-like). Powerful with Sunny day, and is learned by level up (although I would have a grass or fire type with sunny day, like Cherim, or Magmotar)
Foresight or Drain Punch:
Foresight is a move that lets Fighting and Normal type moves hit Ghost type Pokemon. This works well with Lopunny, because it's a Normal (when mega evolved it's a Normal Fighting type). So Hi jump kick can hit Ghost types. Drain Punch is a Fighting type move (STAB when Mega evolved) that steals HP from the target, and gives half of it back to the user. This attack does more damage with the Big Root.