Vehement Idol appears in the Adamah Block of Tartarus, from floors 229 to 235. It will be accompanied by a Grand Magus, discouraging the use of multi-target attacks against either. They will later appear in the Monad Depths as one of the shadow types there.
Persona 4
Vehement Idol appears on Magatsu Inaba floors 1 and 2 within the Midnight Channel. It will attack the party with Ice skills or use Diarama to heal its allies. After being defeated it may drop Calm Marble. Selling 6 Calm Marble will unlock the 1000-Stud Coat male armor in the shop.
In Golden, it appears on the floors above. It may drop Sphalerite for trade at Shiroku Pub.
Persona Q2: New Cinema Labyrinth
Vehement Idol appears on Blocks 3, 4 and 5 in the Theater District. It attacks with single- and multi-hit Wind and Electric attacks. When defeated, it may drop Idol Cache and Idol Veil. Idol Cache is used to create the Queen's Whip for Ann. Idol Veil is used to create the Misericorde for the P5 hero.