Bavlorna's Temporal Flytrap (D)

You conjure an anomalous 10ft cube of slow time on an unoccupied surface within range. Any creature that can't see the area at the time the spell is cast must make a Wisdom (Perception) check against your Spell Save DC to recognise the terrain as hazardous before entering it.

The first creature of Medium size or smaller that enters the anomaly's space must make a Constitution saving throw. On a failure, at the start of their next turn, their speed is reduced to zero, and on their turn they can use either an action or a bonus action, not both. At the end of their turn, they can reattempt the saving throw to end this effect.