EOS circles the combat arena from a great distance, rendering beam lasers completely ineffective. EOS also has massive health and shield pools, approaching the levels generally reserved for raid bosses. Its offensive capability is extreme as well, and can easily send Vault Hunters into Fight For Your Life very quickly. During the battle, bugs and glitches will constantly spawn, and are often best left alone until needed to provide a Second Wind.
EOS has a number of main attacks:
- Moonshot Cannon: This attack will fire a number of projectiles streaming at the Vault Hunters
- Eye Laser: The Eye Laser is EOS's most devastating attack, and can almost immediately down any Vault Hunter who takes the full brunt of it. The firing of this laser does present a lucrative opportunity to the Vault Hunters, though - from the time EOS's Eye starts opening to prepare for the strike, until it closes shortly after finishing the attack, the Eye is EOS's single critical hit area, so Vault Hunters are encouraged to attack that area when given the opportunity.
In addition to its larger attacks, EOS has multiple turrets attached to it. These start out by firing ion blasts at the Vault Hunters but later start firing homing missiles as well. The turrets are vulnerable to corrosive damage, but like EOS they have a massive health pool, and Vault Hunters might not find it worth it to take the time to destroy them.
Once EOS's shields are finally depleted and it takes actual health damage, EOS will eventually disappear from the arena for awhile to recharge its shields back to full. This will generally happen at least twice during the battle. While charging, EOS will generate large holographic images of Lilith and other allies, attempting to discourage and demoralize the Vault Hunters. These images do not otherwise interact with the battle, and can be ignored.
Also during the shield-recharge periods, harder versions of bugs and glitches will start spawning, including Badass Glitches which have reflective shields which can quickly down a Vault Hunter if fired into. During the final round of battle with EOS, these heavier mobs will continue to spawn to further antagonize the Vault Hunters, in addition to EOS stepping up its aggressiveness. The Badass enemies spawned during the final stages will often need to be addressed, rather than letting them be.
Once EOS is finally defeated, 5H4D0W-TP will appear on its throne, lying on its back, the H-Source ready to be plucked out. 5H4D0W-TP will blow a raspberry and generate a large pool of good loot, including Moonstone, glitch and purple items. After the main bulk of the loot has dropped, a final legendary item is guaranteed to spawn, accompanied by another raspberry sound.
- Main article: System Shutdown
- When fought during the story mission System Shutdown, EOS will always reward a random legendary item upon defeat. However, any subsequent fights do NOT guarantee a legendary item. On the relatively rare occasion a legendary item is not rewarded, up to four purple items and four Moonstone clusters are rewarded instead.
- If Vault Hunters have approached the ECLIPSE/EOS fight either underleveled or without extensive gear preparation, EOS can be extremely difficult and time-consuming to defeat. This is partially due to the immediately-prior fight against ECLIPSE being a difficult fight in and of itself, often depleting much-needed ammo reserves prior to EOS's sudden appearance, and partially due to EOS simply withstanding and dishing out substantial amounts of damage itself. It is possible for the fight to last upwards of half an hour in these circumstances.
- Despite this, it is also possible for EOS to be defeated near-instantly, utilizing certain character and gear combinations and/or exploits. Some methods of dealing damage to EOS using these combinations/exploits inflict so much damage that it is possible to bypass multiple (if not all) phases of the fight, effectively cancelling its usually mandatory shield recharges.
- Unlike ECLIPSE prior to it, fighting EOS in co-operative play is actually easier than solo attempts, as EOS splits its attacks amongst the multiple Vault Hunters. This is especially useful if EOS uses its devastating Eye of Helios, as if the targetted Vault Hunter dies, the remaining Vault Hunter(s) can remain in the fight, ensuring EOS won't respawn with full health and shields.
- EOS is prone to several glitches, which can occur at any point during the fight. The first glitch listed below will always happen, the ones following it may happen:
- During the third and final phase of the fight, EOS will always materialize in a static line of sight, rapidly spinning to face its targeted Vault Hunter once it is fully visible. It will remain facing this angle for the remainder of the fight, however its model will instantly flip a full 180 degrees whenever it passes behind the centre of the arena.
- The Eye of Helios and Moonshot Cannon may disappear entirely, effectively removing most of EOS's offensive capabilities.
- During the phases where EOS vanishes and its shields recharge, the Eye of Helios/Moonshot cannon and EOS's various cannons may not disappear. While the Eye of Helios and Moonshot are not utilized during the occurance of this glitch, the laser/rocket pod cannons WILL continue firing.
- EOS may suddenly reset rather than reappear following a phase in which it recharges its shields - completely refilling its health as well. It is also possible for it to simply not reappear at all, making it impossible to finish the fight.
- Upon death during single player, which causes EOS to respawn with full health and shields, it may reappear in a location far away from and not utilizing its regular movement arc, making targeting it either extremely difficult or impossible.
- In Greek mythology, Ēōs is a Titaness and the goddess of the dawn, who is the sister of Helios