Xero

Xero is a Warrior Dream boss in Hollow Knight.

Lore Xero was a warrior of Hallownest who believed that strength would always allow him a bright future. When his mind was infected, he hoped to fight against the plague with violence. Fueled by the same hope, he turned against the Pale King, for which he was executed. Xero was buried in the Resting Grounds, his tomb a reminder to any who would betray the King. When his spirit awoke, he still could not see the wrongness of his actions and instead believed his demise was the result of a doomed fate.

In-game events Xero's spirit appears to the Knight once they acquire the Dream Nail. He accepts their challenge to mock his own fate. Once defeated, Xero finally acknowledges that his actions against the King were irrational. The spirit confides to the Knight its faith in their bravery, before shattering into 100 Essence to be collected by the Dream Nail.

Behaviour and Tactics Xero only uses one attack:
 * Nail Cast: Xero spawns 2 glowing nails. While floating around, he constantly shoots out one of his nails in the Knight's direction and draws it back. He shoots a nail every 1-2 seconds. Coming into contact with the nail while it is being drawn back still deals damage. At 50% HP, Xero spawns 2 more nails, and his attack rate increases, with only 0.75 seconds between each Nail Cast attack.

Dashing, especially Shadow Dashing, is a very helpful tactic for dodging Xero's attacks. To damage Xero, Nail Arts, especially Great Slash and Dash Slash, are useful. The Spell Howling Wraiths/Abyss Shriek can deal a lot of damage, but Xero bounces around and may not take all the hits. The Spell Vengeful Spirit/Shade Soul is very useful against Xero because it has near infinite range and it can hit more than once in a single cast, especially when fired in the same direction Xero himself moves.

Healing without Charms is safest when the Knight dodges a nail and puts themself on the opposite side of Xero's path, often causing the returning nail to miss. In the second Phase, the Knight must begin healing before the nail reaches the end of its range to have enough time to heal. The Quick Focus and/or Shape of Unn Charms can help the Knight heal.

The Knight can heal safely by running off the platform and going to the far left of the area, where Xero's attacks do not reach, or by running under the platform. Note that this kind of healing is not possible when fought in Godhome.

Location Xero can be found in the west part of the Resting Grounds.

Trivia
 * His grave message used to read "Here lies a Traitor", which was changed to the current message ("Cursed are those who turn against the King.") after the public release version 1.0.2.8.
 * This has, however, not been changed in some translations of the game.

References

Ксеро Xero Xero Xero