Chozo Ghost

From Wikitroid, the Metroid wiki

Chozo Ghosts are Chozo spirits driven insane by the corruption of Phazon. They stalk the Chozo Ruins and can be found in religious rooms and the Life Grove in Tallon Overworld. The Phazon corruption has marred their sanity, causing them to lash out at even Samus Aran, who would ordinarily be an ally. They are difficult to defeat without the X-Ray Visor due to their ability to turn invisible unless attacking. In addition, they are invulnerable to all weapons except the Power Beam and Super Missiles. Their charged attacks will leave Samus vulnerable for a short time, as it causes her Power Suit to temporarily short-circuit. They are encountered in places sacred to the Chozo. It is unknown what becomes of them after Metroid Prime is destroyed, and thus the Phazon as well on Tallon IV, though it is likely they eventually faded and then "moved on". Chozo Ghosts also assist in the defeat of Meta Ridley, blasting the cyborg with lasers and then opening the gateway to the Impact Crater for Samus. When charging they are highly vulnerable to super missiles.

They are also seen in a Diorama in Metroid Prime 3: Corruption, though this may not have any canon significance.

[edit] Trivia

The music heard when fighting these ghosts is used in Metroid Prime 3: Corruption as the Metroid Battle theme.