Before the retreat horn sounded, when Arther's army was still in a heated battle with John's force, Jack's regiment similarly fought a fierce battle.
While Arlcard's black fog held the encircling army at bay on one side, Jack's force went to the opposite side, killing everyone they passed through. Arlcard cast his Perpetual Sword of Death and increased the killing pace. The spell's black energy swords zoomed around the battlefield, hitting enemies while sparing friendlies. It was an ultimate large area offensive and support spell. The enemies couldn't concentrate on facing their foes because they kept on getting stabbed by these black energy swords.
The Ice Fiend Demon's passive icy aura also only affected enemies, sparing allies. This caused the fighting to be easier as the enemy's movement became slower.