Cosmic Rot

You invoke terrible cosmic forces upon a creature you can see within range, causing the decay of body and mind.  The target must make a Constitution saving throw.  On a success, the target takes 4d6 psychic damage and 4d6 necrotic damage.  On a failure, the target is affected by cosmic rot.

While affected by cosmic rot, the target has disadvantage on attack rolls and ability checks.  At the start of each of the target's turns, the target takes 3d6 psychic damage and 3d6 necrotic damage.  At the end of each of its turns, the target must make another Constitution saving throw.  On a failure, the target's Wisdom score is reduced by 1d4, to a minimum of 1.  If this spell reduces a creature's Wisdom score to 5 or lower, the creature gains a form of short term madness.  If this spell reduces a creature's Wisdom score to 1, the creature gains a form of long term madness, which replaces any short term madness.  After three successes, cosmic rot ends on the target.  A Greater Restoration spell cast using a spell slot of 7th level or higher can also end cosmic rot.