Phantoon is the boss of the Wrecked Ship area in Super Metroid. It is a ghostly phantom, resembling a bulbous severed head with a single eye in its maw that eerily follows the movements of Samus during the fight. Phantoon is one of the four main bosses you need to defeat in order to open the way to the Space Pirate base, Tourian, and confront Mother Brain.
When Samus faces Phantoon, it will fly around the room and generate rings of blue fire, which it will hurl at Samus as well as using it as a shield to stop Samus from getting too close. All of Phantoon's body is ethereal and cannot be harmed, phasing in and out of sight and appearing almost anywhere to attack Samus. When it disappears and blue fireballs start to bounce around the bottom of the screen (that can be destroyed for health and missile pickups), its the sign it is about to materialize for a split second, allowing Samus to fire charged shots, missiles, or super missiles at its weak point, its eye. Using super missiles is effective, but will enrage Phantoon, who will materialize at the top of the screen and send wave after wave of flames at Samus. After a grueling battle, Phantoon will eventually die (again?) and power to the Wrecked Ship will be restored, allowing her access to more of the ship.
Metroid: Other M
Phantoon also appears in Metroid: Other M as a special final boss after the credits. As the player reaches the end of the epilogue, It appears outside of the Bottle Ship and breaks its way in through the windows of a large observation deck. It once again spawns flaming eyeballs as well as floating cyclops hands. To defeat it, Samus simply shoots charged shots or missiles at its solitary eyeball until it explodes.