Both of these Shadow Souls, the Abyssal Knight and the Revenant King, were handpicked by Asher from the Ten bosses he had faced so far. These two stood out as the most resilient and challenging adversaries, having lasted the longest against him.
As for the other bosses, Asher utilized his Infinite Fusion ability to merge their essences into these two, enhancing their power and abilities with each fusion. Now, both the Abyssal Knight and the Revenant King were formidable entities, nearing Asher's own level of strength. They also inherited a variety of abilities from the fused bosses, making them versatile and lethal in battle.