I initially thought `eurgh`, but I assume you are trying to simulate `night-vision ` camera with the green overlay. Not a bad effort, however I would of added a bit of noise and a vignette as that would give it a better NV camera effect.
Nice blending to of multiple heads to make the three headed dog, Cerberus. This image has strong potential but that greenish cast really drags down the impact. I am wondering why the choice of green? Green is a spring color - symbolizing life. The environment of Hades is just the opposite. The greenish cast also does not allow the black pelt or fur of Cerberus to visually pop off of the background because even the tones and highlights of the fur are greenish in nature. I believe a more rock tones barren color cast for the backdrop...maybe even venture into some deep dark reds (to allude to the concept of hell) to make the environment this creature lives in more believable. But I would not put that color cast on the dog - you want it to stand out on it's own. I like the red eyes but I feel you could have gone more with some further details to make him look fierce and menacing. My two other suggestions to make him look fearsome is to add sharp pointy teeth and to shot the picture at a lower angle to give the impression of menacing, towering over us size.