Phantom

Phantom Guardians, also referred to as Phantoms, are enemies from The Legend of Zelda: Phantom Hourglass. These shady defenders can be found throughout the Temple of the Ocean King. Phantom Guardians have near-impenetrable armor that cannot be overcome by any traditional weapons. Near the end of Link's adventure, he obtains the Phantom Sword, the only known weapon powerful enough to kill them. Large boulders and pits are also effective against them. Link can use the Bow to fire at the weak points on their backside to stun them for a short period of time.

To avoid the Phantoms, Link must sneak around them, so as not to be seen. If spotted, he must quickly have to run to purple tiles called "safe zones" that prevent the Phantoms from seeing or attacking him until he moves away from the tile. An attack from a Phantom deals one heart of damage, in addition to draining 30 seconds worth of sand from the Phantom Hourglass, and returning Link to the beginning of the floor.

There are a total of four types of Phantoms in the game, but only three types of Phantoms are found in Adventure Mode: the most common variety are blue Phantoms, the slowest and most basic type. They are typically found in the earlier floors, or, in the later floors, standing in one spot guarding a switch or path. Red colored, or "Swift" Phantoms, are a bit faster than the blue Phantoms, and are therefore much more dangerous. Gold Phantoms are slow, but when Link is spotted, all Gold Phantoms on the current floor instantly teleport to wherever Link is. These Phantoms carry axes instead of swords.

The only type of Phantom that does not appear in Adventure Mode are Silver Phantoms. They only appear in Battle Mode, where a player must control three of them to hunt Link. When playing Battle Mode, the Phantoms look different from the ones in Adventure Mode; however, they funtion the same way Swift Phantoms do.

The Legend of Zelda: Spirit Tracks
In the trailer for Spirit Tracks, a clip is shown of Link working in conjunction with what appears to be a Phantom Guardian. It is shown following directives given by the player via the touch screen, such as diverting and fighting enemies and walking unscathed through a barrier of fire in order to reach a switch that deactivates the barrier. It has been confirmed these are phantoms on a zelda website