Toxic Rebuke

You point your finger and send a stream of toxic slime at the creature that damaged you. It makes a Dexterity saving throw. Failure: 2d10 Poison damage immediately, and its movement speed is halved until the end of its next turn. Success: half as much damage, no effect on movement speed.

Using a Higher-Level Spell Slot. The damage increases by 1d10 for each spell slot level above 1.