Here's what is happening with the blackness: Grass in real life is slightly transparent, or at least some of the light goes from one side reaches the other side, brightening it. In forward rendering that can be simulated (very simplistically) with the subsurface scattering setting in random-dir mode, in screen oriented grass mode the lighting is already faked to look good, so it's not a problem either. In deferred rendering, Unity handles the lighting by itself, so there isn't really a way of fixing the dark part of the models. I believe (I'm really not 100% sure myself) that the grass looks so dark compared to other objects in the scene, because the blades of grass have a lot of overhang, e.g. they are oriented towards the bottom of the world where ambient light is a lot less. I'll keep looking into this problem, but right now you should either use forward rendered grass, or play around with ambient and additional lights. About the additional lights: I would personally try to create a script that adds fill light to your scene, for example let the light have the opposite direction of your sun light. You could also try adding multiple weaker lights and change their color for each time of day. Just to make sure: did you delete the old grass folder before importing the new version? I'm a bit confused that it happens in your project, but not in a newly created one. Can you try using the deep profiling to see where the performance cost is coming from?