The Ultimate Abyss can absorb a substantial amount of fire and can be difficult to beat without understanding his attacks. Whenever his back opens, that's the cue he's about to teleport. When he does warp, he tends to appear directly behind you so fire at him to interrupt his lunge. Eventually, the Ultimate Abyss will start leaving an afterimage whenever he teleports, in an effort to trick you into attacking thin air; the real mutant will always emit purple smoke in this instance and mostly appears behind you when he does this.