In this scenario you get to pick any power you want except for absolute or meta powers. However as the omnipotent being I want you to pick the downside of having said power. Once you pick that will be forever enforced. The more powerful the power is the much larger and horrible the price shall be. If it's a basic power then the price shall be small and not that bad. Basically what I am saying is make sure the price is fair and balanced. Also choose wisely on what power you want as long as it doesn't break the rules.