Anchor Fog

You summon a diaphanous curtain of magical fog with a leaden density, which weighs down greatly all creatures and objects it envelopes.  The fog spreads across a 20-foot-radius, 10-foot-high cylinder centered on a point you choose within range, blocking vision and movement within the affected area.

While in the fog, a creature's speed cannot be greater than 5 feet per round.  For creatures who are slowed by this spell, difficult terrain does not require extra movement to traverse, however, a creature must make a Dexterity saving throw each turn when they begin their turn in, or first move on to a square of difficult terrain, falling prone on a failure.  Creatures slowed by this spell can stand up from prone without using any movement, but must succeed on a Strength check against your spell save DC in order to do so.

The area of the fog is lightly obscured.  Ranged weapon attacks passing in or out of the fog have disadvantage.  The fog can be dispersed by a strong wind in 1 minute, but otherwise lasts for the duration.

At Higher Levels. When you cast this spell at 5th level or higher, the radius of the cylindrical space the cloud occupies increases by 10 feet per slot level.