In Infinity Blade I, when you choose to go down to the dungeon, the scene right before you head up the stairs to the elevator to the God King, there's a stone with the infinity blade shape on it.
I learned in Infinity Blade II that this is some sort if lock and key mechanism, so what gets unlocked?
When you have the Infinity Blade equipped and you "examine" the sword shaped lock in the centre of the dungeon, you place the sword inside and it descends into the floor. This unlocks three more doors in the dungeon, each of which leads to a challenging boss fight with one of The Deathless Kings: Ealoseum, Gortoel and Kuero. Once you've defeated each of these bosses, it unlocks a final showdown with Zero Mech and an alternative ending if you prove victorious.
