A God at the Gate: Fourth Track.

As a consequence of the spell cast by one Ethan Rayne, Chaos mage extraordinaire, over the costume chosen to wear on All Hallows Eve by quintessential "normal" guy, and walking paradox, Xander Harris, the good Mr. Harris the younger gains and retains the abilities of the infamous youngest Summers brother: Vulcan.

Xander keeps the aforementioned abilities, such as they are described in the "Superpowerwiki" web-page, with absolute control over them and complete and intimate knowledge of how to use them to their non-existent limits.

Such an incident is peripherally noticed by such groups as the Ascended Ancients and the Asgard, who proceed to hint and direct Stargate Command towards Sunnydale in search of the cause of this "disturbance".