"cheat-code away from finding the hidden hentai tentacle level."

Continuing on from the comment I left below...there's no cheat code involved. You just get 11 of the 12 Core Fragments (the 12th is hidden in said level), then use your cat form abilities to climb up the shaft to the right of the warp to the Frozen Wastes. There you find the entrance to the Twisted Nether, aka the hidden hentai tentacle level.