Wren's Spellwarping Curse

You place a curse on a creature you can see within range. The target must succeed on a Wisdom saving throw or becomes cursed for the duration of the spell. While cursed in this way, the creature takes 1d8 + your spellcasting ability modifier (minimum of 1) psychic damage each time it casts a spell that deals damage or forces a creature to make a saving throw. If the target attempts to cast Remove Curse on itself, it does not remove this curse.

While you have this spell prepared or choose it as one of your spells known, you become aware of any creature that is observing you from afar with magic, such as through a Clairvoyance, Dream, or Scrying spell. While a creature is observing you in this way, you can cast this spell on that creature as if you could see it and it were in range.

If you cast this spell on a creature that can’t cast at least one spell, the spell fails, and you are aware of why it failed. If the target of this spell has ever targeted you with a harmful spell against your will, they have disadvantage on the saving throw and the effect is permanent unless removed by a Remove Curse or Greater Restoration spell, or similar magic, by someone other than themselves. You can also choose to end the spell by using an action to dismiss it.

Credit: Created by the World's Beyond Number team for their homebrew Witch class, as seen on "The Wizard the Witch and the Wild One".