Insanity Manipulation (others) – The ability to cause mental illness.
The D&D universe has several characters that create different types of mental disturbances including Despair (Creature Collection II. Dark Menagerie), Fell Taint (D&D 4th Edition – Monster Manual 2) and the Shadow Jester (Creature Collection II. Dark Menagerie).
Abyssal Rotfiend – D&D 4th Edition – Monster Manual 2
Delirium (Vertigo) was Delight and is more less the goddess of madness in the Sandman universe (The Sandman – Brief Lives V7). Delirium is mad and can cause madness in others.
Why did delight become delirium?
In the beginning of the universe the realms of imagination and reality had porous borders and moving back and forth between these realms caused delight. When the borders became solid, the movement between reality and imagination became delirium.
Interestingly, Delirium has the power to grant sanity and helps a little girl become sane in The Sandman-Endless Nights.