The Staircase of Punishment

You target one creature you can see within range. It must succeed on a Charisma saving throw or be sent into a pocket demiplane created by this spell. This demiplane contains an infinite staircase with no bottom or top - just endless stairs. The walls on either side of the staircase reach up infinitely to a night sky. The sky has stars and there are glowing lines through the walls and stairs to cast dim light in dark red tones. The walls and stairs seem to be made of an indestructible black stone and have no traction - they are incredibly slippery and it is impossible to stand or move without slipping. The air and even gravity seem to work differently: flying and hovering is impossible and there seems to be something that prevents magic, as if the whole demiplane contains an antimagic field.

A creature in ths plane cannot fly, hover, cast spells, use magic items, activate any magical effects or abilities, is rendered prone even if normally immune and will spend every moment in this place slippng and falling down these infinite stairs non-stop. On their turns the creature cannot use movement of any kind or take actions and will just be falling down the stairs. They must make a Dexterity saving throw to try and control some of their endless falling down the stairs: on failure they take 6d8 magical bludgeoning damage and on success they take only half of that. At the end of their turns the creature can make a Charisma saving throw and on a success the spell ends.

When the spell ends the demiplane vanishes and is unmade and the creature is returned to the space it occupied when the spell was cast or if that space is occupied then the nearest unoccupied space. They will land prone.