Chronal Bubble

An immobile dome composed of chronal shards springs into existence around an area you can see. The bubble can be up to 10 feet in diameter

When you cast the spell, any creature that is completely inside the cage's area is trapped and cannot move. Creatures only partially within the area, or those too large to fit inside the area, will have the effects of the spell only affect the parts of them inside the bubble, which are immobile.

A creature inside the bubble must succeed a DC [spellcasting DC] wis save or else take 4d6 necrotic damage each turn spent in the bubble. For each turn spent in the bubble their speed is reduced by 1d4+[spellcasting modifier] 

This spell can't be dispelled by dispel magic due to its nature as a warping of time itself rather than any sort of magic.