Angry Itch

For the duration of this spell, you cause a targeted humanoid's legs to bleed, causing them to have extreme trouble moving, almost as if they had to relearn walking. You deal 2d8 necrotic damage when you cast this spell. A targeted creature may make a Constitution saving throw to halve the damage. If you maintain concentration on this spell, you may use a bonus action on your turn to deal this damage again.

At the beginning of an affected humanoid's turn, they must make a Constitution saving throw against your spell save DC. On a successful save, their movement speed becomes 10ft for the rest of the round. On a failed save, their movement becomes 0 for the rest of the round. Effects that increase movement speed do not affect this spell's reduced speed. 

A creature affected with this spell must make an additional Constitution saving throw to take the Dash or Disengage actions.