A partially nude feminine looking demon that is summoned by breaking a Dark Crystal. It appears in the game Castlevania: Lords of Shadow and makes a cameo appearance in Castlevania: Lords of Shadow 2.
It first appears in the fifth level of Chapter II, Agharta. Gabriel witnesses a mysterious girl summoning it (via a Dark Crystal) to kill a nearby Cave Troll before she quickly and nimbly climbs one of the ruined buildings nearby and, without saying a word, beckons Gabriel to follow. Later on, Gabriel can summon it via the Dark Crystal sub-weapon.
After becoming Dracula, Gabriel kills one of these demonesses when it was used against him during a battle with Victor Belmont in Castlevania: Lords of Shadow 2.
One possible origin for these strange creatures can be seen in The Clockwork Tower, where a statue of a man appears to be dragging an angelic woman into flames - the angel's belly has an identical marking to that of the crystal demon.