Turok

First of all this achievement is misleading, you do NOT need to kill a teammate, so ignore that part. A creature is either a bug (such as a scorpion) or a raptor, these can be found on most maps but certain ones require you to active a switch. As for the enemy, you can kill them with whatever weapon you deem fit. Finally to kill yourself just throw a grenade at your feet and step on it. It is also possible for this achievement to be boosted with a friend if you join the same player match.