Dungeon of Id

You target a creature within range and the target must make a Dexterity save, the target can choose to fail. On a fail, the target is sent to a demiplane in shape of a dungeon room with 3 doors, each door leads to the same room that they started in. On a successful save nothing happens and the spell slot is wasted. 

The dungeon is made of whatever piece of material the component is made from. At the time of casting you can choose to spend an extra spell slot and inhabit the dungeon with a monster of cr equal to the spell slot you spend. This monster can be of any type the caster wishes. The caster chooses the monster in the dungeon, the monster is hostile to the target in the dungeon and will attempt to kill them or be killed themselves. If the monster is killed its body disintegrates and leaves nothing behind, the caster is aware of when the monster is killed or if the monster kills the target.