Due to Ishtar's and the Skeleton Grand Archer's harassment of the Red-Eyed Terror Mantis, the Mosquitoes were able to take advantage of the situation and collectively bombarded the Mantis with Venomous Sprays that whittled its health away.
The other Insects who realized that their leaders were losing the battle decided to shift their attention to the Skeletons that had appeared out of nowhere. However, Diablo stood in front of his subordinates and fought with Blood Moon in hand.
Although two more Skeleton Fighters died during the collision, Diablo was more than enough to hold off several enemies at once. After all, he was a Rank 2 Monster, and he had a Mythical Weapon on hand.
The Mosquitoes had figured out that the Skeletons were on their side, so they used this opportunity to deal significant losses to their enemies.