Adrian Gecko with "Forbidden Beast Nibunu" and "Forbidden Beast Inun".
"Forbidden Beast" known as "Sealed Beast" (ふういんじゅう Fūinjū) in the Japanese version, is an archetype used by Adrian Gecko in the Yu-Gi-Oh! GX manga. Many of them resemble armless reptiles with effects linked to the "Forbidden Mantra", which holds their power. Their name change from the Japanese to the English Version seems to have been inspired by that of Exodia, which Adrian's anime counterpart used.
The "Forbidden Beasts" effects require the "Forbidden Mantra" in play, otherwise they are nearly powerless. The only exception to this is "Forbidden Beast Nibunu," which is also the only "Forbidden Beast" monster that has arms. When "Forbidden Mantra" is in play, their deadly effects of destroying cards come into effect. Some of them also focus on Summoning from the Graveyard and getting "Forbidden Mantra" onto the field.