I have not tried out Cosplay Pikachu yet, but I have excelled with other pokemon. Here's what I think would help you.
Replace Dig with Thunder Wave and Flying Press with an alternative appeal move: Slam, that can work with Strength during the contest. (Can't use the same move twice or it doesn't go well). Thunder Wave is not a tough contest move, however because it startles all other pokemon before you, that will prevent the other contestants from moving. As for strategy, I would use in the following order this: 1. Strength or Slam, 2. Thunder Wave, 3. Strength or Slam (whichever one you didn't use before), and 4. Wild Charge. The last move has great appeal and you won't need to worry about being startled during that turn. Hope that helps!
I need an opinion on if this below would work well against the elite 4 on alpha sapphire.
Meganium @ Leftovers
EV: 252 Hp / 252 Spe / 4 Sp.A
I have no interest in competitive battling other than just having fun with the sets. Any opinion or extra thoughts would be appreciated!