The demons advanced, carelessly, one might say, empowered by their leader, a monster feared far and wide. They advanced at a hopping run, flying only short stretches or close to the ground in order to follow the trail. Demonic cavalry rode along the flanks, Vrocks, Babaus and the Balor forming a loose formation in the center.
The mutants lay in waiting, poised and ready, their only chance being the element of surprise and quick flanking action on the leader - if they could take down the balor, or at least occupy him in melee without a chance to effectively attack them from range with his magical abilities, then the other demons might waver and flee.
As Thor watched, the play unfolded. The demons strode into the trap, their heavy steps easily alerting the buried ambushers. The sand exploded forth in a flurry of claws and teeth, the attackers immediately singling out the Balor and flanking him, the mutant Vrocks taking the brunt of the fighting, while the Babaus, Troll, and sand hunters engaged the smaller demons.
However, to their dismay the mutants barely grazed their pursuer, at least the Balor was practically immune to their attacks. He roared with laughter, and began returning blows with sword and whip, but, to his irritation, the thick hide of the mutants severely lessened the impacts of sword, whip and claws, and even when the Vorpal sword hit hit home and severed a head, then there were enough others to keep the target alive.
The mutants attacked again with renewed effort, putting more force into their blows, and with that managed to graze the flaming demon. But even then, this was sadly ineffectual. The other mutants were quite powerful agains the smaller demons, but even then, many weak bites against the demon's inherent resistance to damage made the overall effect quite disappointing.
And then the Balor roared again, and a second Balor appeared and joined the fray. And after after a while of back and forth, the Balors finally decided that melee was not the way to go: Calling upon their inner magical powers they called forth dimensional rifts that disrupted the entire forms of their targets. Within a few seconds, two mutant Vrocks imploded in a spray of green blood.
That turned the tide. With their most powerful fighters so decimated, the mutants were demoralized. The demons broke from the melee and tried to organize a retreat, but it was a lost cause. Whenever they retreated, the cavalry charged the weaker mutants, and some demons teleported into their path. Once they were out of melee, the Balors followed up with more magic, and soon many of the smaller mutants were jabbering mindlessly or otherwise incapacitated.
Finally the remaining teleport capable mutants took off, with cries that MOTHER would avenge them. What remained was a battlefield still busy with mop-up, with the non-demonic mutants slowly killed off one by one as they fled or stood. The demons had lost a few of their smaller brethren, but the enormous power of the Balors had won the day.
