Black Hole

A black hole springs into existence on a point of your choice that you can see within range. Its gravitational force spans a 15-foot radius sphere centered on that point. each creature that is completely in that area must make a Strength saving throw. 

Whenever a creature enters the spell's area or starts its turn there, it must make the saving throw. Moving 1 foot in the area costs 5 feet of speed

at the start of each of your turns until the spell ends, the radius of the sphere increases by 5 feet