The Thoraxe is a large insect-like axe located in the Beetle Lair. If wounded by the Thoraxe, a kombatant's health would slowly drain. The reason for this is that it is made of Cyanidium, a poisonous metal. A wall carving in the Beetle Lair was of the ancient warrior demi-god, the Death Knight, who used the Thoraxe as his weapon.
As mentioned above, the Thoraxe was located in the Beetle Lair stage in Mortal Kombat: Deception. It was available to be picked up and used by players during a match.