Dariastern's Well of Shadow

You target a Huge or smaller creature within range that has a shadow and stands on solid ground (though it need not be on the literal ground and could be on top of a house). The target's shadow becomes a black pit that leads to a pocket plane within the Shadowfell. The target's pulled into its own shadow, appearing within the demi-plane. The target remains there for the duration or until it escapes.

The target's shadow remains in place while the target's gone and is the same size as the target. If the target moves within the demi-plane, the shadow moves similarly. The target can only move horizontally while within the demi-plane. The first time on a turn, the shadow moves into the space of another creature of equal or smaller size to the target, the creature must make a Dexterity save or also be pulled into the shadow, appearing in the nearest unoccupied space to the initial target within the demi-plane.

A creature within the demi-plane can make a Wisdom save at the end of each turn, escaping on a success. The spell ends with the original target escaping, freeing all other creatures trapped within the demi-plane, and causing the shadow to rejoin the target. A creature that escapes appears in the nearest unoccupied space of the shadow but is frightened until the end of its next turn as it reels from the horrific experience.

Creatures native to the Shadowfell aren't frightened by this spell.