what if:
the infiltrators had a sniper rifle- unsilenced, very loud, plagued by horrifying inaccuracy problems if the player was moving at all (to discourage using it to directly attack), had very little ammo and was generally unwieldly in every way except for the fact that it did huge damage
the infiltrators had a knife that could instantly kill, but is generally too short ranged to use as a direct combat weapon (especially against the guard's horrible death machines)
any rounds fired by the infiltrators dropped debris that lingered for some significant time and stuck around long enough for anyone to be able to see them
any player hit by a bullet would not only cause a burst of blood to splatter on the floor, but for the player to drop debris for a little bit
infiltrators have a 'cleaner' item that can clean up debris to cover their tracks, but made a loud noise (a vacuum?)
the guards, when using their pistols, take out a riot shield and can defend themselves from things coming from the front
instead of AKs, the guards have light machine guns. this is mostly for coolness reasons
guards regenerate health quickly and have 1.5x normal health but are otherwise generally normal
infiltrators, on the other hand, regenerate health very slowly and have normal health but move only marginally faster then normal
Poll