Greater rotfiends tend to be larger than the garden-variety rotfiends. The first one Geralt encounters is located in the cave under the waterfall southeast of the village of Flotsam, guarding a deposit of ostmurk.Later, in the witcher finds more of these beasts in an old mine in the village of Vergen. When killed, Greater rotfiends explode, sending out potentially lethal venom. See: The Witcher 2