Your task is simple:
Grant the wish made by the user above you, while at the same time corrupting it in whatever way you wish to make it different than what the previous user originally intended.
Afterwards, you make your own wish, which in turn will be corrupted by the next user.
USER A: I wish I had a million dollars.
USER B: Granted. You now have one million dollars.
In monopoly money.
I wish I had a steak.
USER C: Granted. It’s made out of rubber.
I wish Batman was real.
I wish I possessed an army with which I could conquer the world.