Did you know that there's an extremely well-hidden cameo in God of War: Chains of Olympus? It's the much deadlier, more ancient Companion Cube, the omega of all cubeforms, capable of kicking serious ass.
Ready At Dawn writes today that the developer, known for its PSP expertise, was "surprised no one has found this one out yet." The dev also reveals how it's done, saying the player must "finish Chains of Olympus in god mode, [with]no upgrades, and collect all the urns of power twice without dying you open up the companion cube as a hidden character."
That makes this a little strange. I've collected every single Urn of Power at least three times over, even the one you can only get using the Basilisk glitch, yet I've never seen this. I'm guessing that's because it's not real.