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.
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.