Amnesic Swarm

A 20-foot-radius invisible sphere is generated where you stood during the spell's casting, and remains there for the duration. When any creature (hostile, neutral, or allied) enters the field, the DM rolls 1d10 to determine which spell slot levels shall be locked from it (10 being cantrips) these effects last as long as the creature is in the sphere, and 30 seconds after the creature leaves the area determined by the spell (either by leaving the area by travel, or the sphere being dispelled). Any currently active spells from this spell slot entering are dispelled instantly upon entering the field, except projectiles.

The creature under the effects from this spell are not alerted to it's effects until it tries to cast a spell of the rolled level.

Any creature can attempt to brute force a spell of the locked value by contesting wisdom against the caster, with disadvantage. Failure of this contest drains the spell slot, as if the spell had been cast, but there are no effects. Succeeding this contest causes Amenesic Swarm to be dispelled, and deals 3d8 psychic damage to the caster (this damage cannot be negated, reduced, or increased).

Casting this spell at higher spell levels causes the radius to increase by 5 ft per level over level 5.

At spell level 8 or above, the radius can be optionally reduced back to 20ft, and creatures entering the field instead roll 2d10 to determine which spell slot levels are blocked to them. (If both die rolls are the same, only one spell slot level is restricted) If this option is taken, casting this spell at spell slot level 9 increases the radius by 10 ft.