Tenser's Stable Slab

This spell creates a rectangular, horizontal plane of force, 30 feet long, 3 feet wide, and 1 inch thick, that begins from your occupied space in a direction and orientation of your choosing.

The slab is able to occupy the space of other objects and creatures. When the slab is occupying the space of a creature, the creature chooses to stand on top of the slab or fall Prone underneath it (no action required). If a creature stands on the 1 inch thick edge, it must make a DC 12 Dexterity save or fall Prone underneath the slab.

The slab is immobile and remains for the duration. It can hold up to 500 pounds. If more weight is placed on it, the spell ends, and everything on the slab falls to the ground.