Wish

Wish is the mightiest spell a mortal creature can cast. You can alter the very foundations of reality in accord with your desires. The basic use of this spell is to duplicate any other spell of 8th level or lower without needing components. The spell simply takes effect. Alternatively, you can create one of several effects: create up to 25,000 gp worth of nonmagical objects, allow up to 20 creatures to regain all hit points and end all effects from other spells, grant up to 10 creatures resistance to one damage type, grant up to 10 creatures immunity to a single spell or effect, or undo a single recent event by forcing a reroll. You might be able to achieve something beyond these examples. The DM has great latitude in ruling what occurs; the greater the wish, the greater the likelihood something goes wrong. The stress of casting this spell might mean you can never cast it again (33% chance) and suffer penalties until you finish a long rest.