By speaking aloud, you can alter reality. Wish can duplicate any 8th-level or lower spell, or even undo cosmic events. The DM determines the effect. Greater effects increase the chance of unintended consequences. Using Wish for effects other than spell duplication causes strain: until your next long rest, you take 1d10 necrotic damage per level of any spell you cast. Your Strength score becomes 3 for 2d4 days. You might lose the ability to cast Wish.