Ultimate wish

Ultimate 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. You don't need to meet any requirements in that spell, including costly components. The spell simply takes effect.

Alternatively, you can create one of the following effects of your choice:

• You create one object of up to 5,000,000 gp in value that isn't a magic item. The object can be no more than 300 feet in any dimension, and it appears in an unoccupied space you can see on the ground. This cannot be used as a material component for this spell.
• You allow up to 200 creatures that you can see to regain all hit points, and you end all effects on them described in the greater restoration spell.
• You grant up to 100 creatures that you can see resistance to a damage type you choose.
• You grant up to 100 creatures you can see immunity to a single spell or other magical effect for 8 hours. For instance, you could make yourself and all your companions immune to a lich's life drain attack.
• You undo a single recent event by forcing a reroll of any roll made within the last 10 rounds (including your last turn). Reality reshapes itself to accommodate the new result. For example, a ultimate wish spell could undo an opponent's successful save, a foe's critical hit, or a friend's failed save. You can force the reroll to be made with advantage or disadvantage, and  up to plus or minus 10. You can choose whether to use the reroll or the original roll.
• You can create a non-legendary magic item.
• You can add a spell to the campaign. You learn/always have this spell prepared no matter your class.
• You learn/always have prepared any 2 spells.

 
You might be able to achieve something beyond the scope of the above examples. You decide one thing that happens. The stress of casting this spell to produce any effect other than the ones above weakens you. After enduring that stress, each time you cast a spell until you finish a long rest, you take 1d10 necrotic damage per level of that spell. This damage can't be reduced or prevented in any way. In addition, your Strength drops to 5, if it isn't 5 or lower already, for 1d4 days. For each of those days that you spend resting and doing nothing more than light activity, your remaining recovery time decreases by 2 days. Finally, there is a 10 percent chance that you are unable to cast ultimate wish ever again if you suffer this stress.