Chozo Ghosts are alien apparitions from Metroid Prime. They were ridden of their living forms by excessive phazon exposure.
Many Chozo that lived on Tallon IV were destroyed by the impact of a Phazon meteor, and even more werekilled by the Phazon that slowly spread. Particularly unfortunate for some Chozo, the phazon warped their minds into phazon corruption. Eventually, the Phazon Killed them, their warped souls still haunting sacred chozo landmark, their old calm chozo minds gone forever.
They are ghostly versions of the Bird-like race of aliens known as the Chozo. They are driven mad by phazon corruption, so they will attack anything in sight, including Samus.
They are quite powerful and are invulnerable to all of Samus's beams except the Power Beam which makes these enemies very difficult to defeat, though they are vulnerable to the Super Missile, which is considerably more effective.