Zone of Lethargy

You select a 10-foot by 10-foot area on a flat, horizontal surface you can see within range which is filled with a faint flow visible only to you. Creatures entering the area for the first time or beginning their turn there must make a Dexterity save or be slowed by 10 feet. This spells ends if you cast it again or if you dismiss it as a bonus action.

You may have two concurrent castings of this spell when you reach 5th level, three concurrent castings at 11th level, and four concurrent castings at 17th level.