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The first encounter with Haos is not an actual battle and the player must navigate a series of platforms and barriers in order to escape in an elevator. Shooting at Haos is pointless and downright dangerous as the beast smashes apart the platforms and failure to keep moving results in an instant death. However, Haos will block the path at certain points and the player must shoot at its face until it recoils. This must also be done quickly, as Haos will crush the platform if no action is taken.
Once Chris and Piers escape to the upper levels of the facility, they are forced to confront Haos directly. The creature has no unique attacks at this stage of the battle and it will simply try to smash the player with its arms. Explosive weapons are effective at fighting the boss, although any weapon will suffice. This battle shouldn't cause the player too many problems and Haos falls rather quickly.
The encounter with Haos in the tunnels is another chase sequence. The player must slide under the bulkheads before they close and stay ahead of the collapsing tunnel. At certain points, Haos will smash its hand through the wall to block the way, its hand must be shot quickly to make it recoil.
In the second half of the chase sequence, Haos pursues the player directly and getting caught results in an instant game over. The player must keep running away from Haos until they reach the next chamber where the final battle takes place.
After Piers injects himself with the C-Virus and weakens Haos with an electrical blast, the beast encases itself in a chrysalid and emerges at at greatly reduced size. However, it is still a dangerous opponent and should not be underestimated. Haos mainly attacks with lunges and swipes, but it will also assault the player with a flurry of tentacle lashes that deal heavy damage. Haos can be damaged with conventional weapons, but attacking its exposed organs is the only way to truly defeat it. Piers can stun the creature with his new electrical attacks, which will enable Chris to target the organs more easily. Once Haos has sustained critical damage, follow the QTE prompts to defeat it.
Hand Smash: Haos will raise its arm up and attempt to flatten the player under its hand.
Arm Swipe: Haos will stretch out its arm and slide it in a circular motion. Staying far away is advised, as Haos' reach is quite long.
Grab: Haos will grab the player and raise them up in front of its face, exposing its skull. It will then crush the player between its fingers. It is an instant kill move.
Tentacle Spread: Tentacles will emerge from Haos's hand and will snake towards the player. They can move around corners and will cause moderate damage.
Tentacle Lunge: Haos will slam its hand down near the player, and several tentacles will slide out and swing into the air. If the player does not move out of the way, they will swing down and knock the player back several feet.
Tentacle Drag: Haos will lunge its arm out and tentacles will fly towards the player. If the player does not move out of the way, they will drag them right underneath Haos, opening up a shot at its organs, but at the same time leaving the player vulnerable to any attack from Haos if they do not flee. This attack can be very difficult to avoid.
Slime Bomb Spit 1: Haos will spit 4-5 green balls of slime at the player in a wide spread. If they connect, they can cause low to moderate damge depending on difficulty, and if they hit the floor, they will slowly grow and eventually explode. They can be destroyed beforehand.
Slime Bomb Spit 2: Haos will do the same thing, but instead will fling them at the ceiling. They will stick and will grow like before, but will not hurt the player unless they walk underneath them, in which case they will drop down and explode. They can be shot down or will explode by themselves given time.
Body Slam: Haos will jump at the player, either from the ground or from one of the platforms, and will cause extreme damage if not avoided.
Injured Attack: When all three of Haos's vital organs have been shot and destroyed, it will flail around as its lower half disconnects from its upper half, and the lower half will slide around quite fast, attempting to either reconnect with the upper half or slam into and claw the player. It explodes within a few seconds if it fails to do either. However, it will do massive damage if it manages to hit the player.
In the drainage chamber where only Haos's upper body is seen, attacking the head with the semi-automatic sniper rifle will speed up the fight, provided your aim is true. The player should try keeping the scope zoomed out, as zooming in will cause Haos's head to constantly weave out of the reticle.
In the final fight, as Piers, Haos can be stunned and damaged with a fully charged electrical blast. However, using normal blasts is wise as they are far more accurate and the player can destroy the organs easier this way.
Haos will spew organic time bomb-esque growths from his mouth. Stay away from these if possible, destroy if necessary.
If you run out of ammo during the final fight, there are boxes placed around the area and the Slime Bombs occasionally drop ammo.