Hidden gargoyle

The Hidden Gargoyle is a Halo 2 Easter Egg that can be found in the Halo 2's multiplayer map, Backwash. This is to signalize the map is old and rediscovered. Clearly Bungie did not try to keep the details all visible

Methods
To find the hidden gargoyle, head over to the Blue Base and look towards the Forerunner structure. The figure is located on the left side of the roof, slightly above the balcony of the structure.