You infect a creature with an arcane disease that unravels the mind. Target creature must make a Sanity saving throw.
On a failure, the target suffers the spell delirium madness. While maddened, if the target casts a spell, it must expend an extra spell slot of any level, a use of 1/Day spell, a Legendary action or other similar ability. If the target doesn't cast a spell on its turn it takes 8d4 psychic damage, and it can’t take reactions or bonus actions until the end of its next turn.
On a success, or if that creature does not possess the ability to cast a spell, the target takes 8d4 psychic damage and the spell ends.
The target can repeat the saving throw at the end of each of its turns. On a success, the madness ends.