Protoss structures and, to a lesser extent, units, draw their energy from a great psionic energy matrix that emanates from Aiur. While a nexus provides a link to this matrix, khaydarin crystal-based pylons are needed to actually tap into the energy required to provide psionic energy to new colonies. Each pylon generates a short-ranged aura of energy, which can provide the power needed by structures and warp gates.
Pylons project a strong magnetic field which makes the ground beneath them impenetrable by "mortal means".
Large clusters of pylons were once used to generate an electromagnetic field that prevented zergspire units from maneuvering. The clusters were based at Talematros, capital of Shakuras, before Infested Duran's forces destroyed them.
The Dark Templar have their own version of the pylon in the form of the monolith. As circumstances grow increasingly dire for the protoss, the dark pylon has entered general use for the protoss alongside the regular pylon.
If a protoss building loses its connection to the psionic matrix, it will shut down until it is reconnected, and new units cannot be gated in if there is insufficient psionic energy to provide them with power. Unpowered buildings will display it when selected, and makes a particular sound instead of the building's own sound.
Along with the shield battery, its the only building in the game that do not leave debris when destroyed (without counting the vespene geyser buildings).
The following section contains information from a previous version of StarCraft II which is no longer valid.
The pylon used to have its own portrait instead of using the protoss racial portrait like other buildings, but by the StarCraft II beta it was reverted to the default protoss "adviser". The old pylon portrait now serves as the mothership portrait.
During BlizzCon 2007, the color of the pylon's crystal would change to match that of the corresponding player's color. This was changed back to the default blue by BlizzCon 2008.
↑ 1.01.1Underwood, Peter, Bill Roper, Chris Metzen and Jeffrey Vaughn. StarCraft (Manual). Irvine, Calif.: Blizzard Entertainment, 1998.
↑No, they cannot move under buildings. The ground is too compacted from the weight of the structure and the Infestor cannot tunnel through. Even Protoss Pylons make everything really hard to move through because a strong magnetic force from the Pylon makes the ground beneath it nearly impenetrable by mortal means.
It's not really practical for the gameplay. You get "units inside units" if the the Infestor could hide under structures which is never a happy place to be. Selection gets difficult, targeting becomes challenging, etc. Cavez. 2009-02-26. (Question) Infester movement under buildings?Battle.net StarCraft II General Discussion Forums. Accessed 2009-02-27.