The true power of God slayer has not been revealed. Godslayer was originally given to Gamora by Thanos to kill the Magus. Its composed of an unknown nigh unbreakable substance. It is capable of killing gods and other vastly powered beings. It has also demonstrated the ability to bring forth and engulf its self in an undefined blue energy.
When last referenced the blade had broke on Thanos' skin when Gamora attempted to kill him after his recent rebirth and upgrade in the Thanos Imperative story arc.