The Illusion Of The Emerald Dragon

You choose 1 enemy to send to a world of illusions. The enemy makes a DC25 wisdom saving throw. If they succeed, they take 5d8 psychic damage and the spell ends. If they fail, they see themselves in a castle with an emerald dragon. The castle is fake and so is the emerald dragon. Every turn while they are in the illusion, they take 5d8 psychic damage but they are sure that it is acid damage. They make the save every turn until they succeed or the spell is dispelled.

Using a Higher-Level Spell Slot. The damage increases by 3d8 for each spell slot level above 7.