This is a very small but very difficult level. The entire level consists of a long stone bridge and the terrain below, much of which is lava, but there is a flat area of rock. Initially the bridge is incomplete, so you have to kill the warlord before you can cross the bridge to the next level.
The best combat plan is to drop off the bridge to the rock below and try to confine your fight to the arch under the bridge.
Hide behind this arch, trying to get the Warlord to stay on the other side. If he flies over the bridge or through the arch run to the other side as quickly as possible. The key is to always keep it on the other side. Youll spend a lot of time hugging the bridge, hiding. Periodically you should strafe past the arch, firing projectiles until you reach safety.