Hellfire

Hellfire is a rare flame created by extracting energy from a tortured soul. Found almost exclusively in the Nine Hells’ deepest reaches, these vile flames burn uncontrollably in areas where souls are gathered.

    Effect: Whenever a creature that is not a devil enters a square containing hellfire or starts its turn there, it takes ongoing 5 fire and psychic damage per tier (save ends). If the creature is bloodied, the damage increases by 5. In addition, whenever a creature takes ongoing damage from hellfire, the creature cannot take opportunity actions or immediate actions until the start of its next turn.
    Usage: Hellfire is common to the Nine Hells and rare elsewhere. Diabolists and those in service to Mephistopheles might know how to create hellfire and use it to ward their lairs.

Published in The Book of Vile Darkness, page(s) 2-28.