What will happen if I generate via QR code, a Pokemon or item that is not in that game?

Question

Let us say I used QR to generate altariaite in x and y

Comments

It will also corrupt your save, beware!

Answer 1

Since that item's effect is not in the game's coding, the item would have no effect at all. You could not mega evolve Altaria in X or Y because Altaria's mega stone didn't exist.