Shade- The regular grunts of the group, able to phase through walls and possess any regular people. They also are also able to throw objects around. However, they are unable to stand the sunlight and will actually fade away if exposed with any source of light, and will actually fade away from existance if they are in the light for too long. The only way to go into the light unharmed is to be possessing someone. You can tell if someone is possessed because the possessed's eyes turn into a shade's Red eyes, and glow.
Light Shade- A lighter, faster version of the regular Shade. I guess you can also call them Young Shades, since they aren't as intelligent as their larger bretheren.
Sorcerer Shade- A shade that is more powerful then your average shade, so powerful it emits a pulsing dark aura as it moves around. They can attack by shooting out a blast of darkness, causing pain and possibly acting like a bullet if it punctures through someone.
And finally, the main supplier of these guys:
A Shade Portal! A inter-dimensional portal to a planet in eternal darkness, the Shades come in from these portals, so you have to find some sort of way to destroy or block the entrance. You can tell there is one in the area because the area it is it is usually grayed-out. What are those two red eyes peering from the portal? You may figure it out if you kill enough of the Shades.