With Axel's impressive flame-thrower trick going on, it was a bit hard for Xigbar to see exactly which parts of the screeching, muddy, flaming mess were still alive and which were well on their way to nothing, so he resigned himself to picking off the few muddy monsters that managed to crawl through Axel's wall of fire, before they could do any damage. At least once they had the small stuff down, they could focus on the big guy. Look like they needed a lot more than one flame-thrower trick to take down that thing.