Add some lighting (you can add some lightning, rain, stuff like that to make it more intense) herobrine could have bended legs and other stuff... Notch too, you can make this more darker and if you add light it should be more focused at herobrine and notch, you should add glowing eyes for herobrine and some monsters (zombies, creepers, skeletons,spiders etc.) the mansion could have lights in it, herobrine should be more at center and add some shadows...
Hope my critism helped!