-To get two of your enemies to fight, get behind one so that the other hits or shoots the first one. After that, step back and they will start fighting each other. They will fight until one kills the other, then it will turn its attention back on you.
-Go to Botmatch, then Coop Game. From here, you can pit creatures spawned with the summon code against each other in whatever instance of the game you want. There are two ways to get the creatures to fight each other until one dies. The most effective method is to enable the fly and invisible codes then summon the desired creature. Then, right click to fly directly above the creature you just summoned. Once you are above the summoned creature, summon another creature of your choice. That creature will fall on the creature below him, and they will begin fighting until one of them dies. Note: This does not work on creatures of the same species, for example a Krall falling on top of another Krall.