Crusius' Mist

You release a cloud of mist into an area within range. Any creature that enters the mist or starts its turn within the mist takes a 10 foot penalty to its movement speed for the duration of the spell, whether in or out of the mist’s area. Creatures within the mist must make an intelligence check that equals or surpasses your Spell Save DC to exit the mist. Attacks going in or out of the mist have disadvantage