"Fly on the wall" mode?

[Equil]

Open your level in the editor, click the grunt/brute, click the "Entity" tab, then tick "DisableTriggers". Now you'll be practically invisible to the enemy, you can stand right infront of him and throw boxes in his face and he won't care. As for the darkness, just give yourself a lantern using script, not much you can do about the blurry vision I think though.