X-2 riddle this time:

Tainted.
That is the reality.
Our sleep has been fitful,
and now we awake.
We shall confront our old master.
In order to combat this new threat,
she must first combat old allies.

Who are we?

A very easy riddle, but I wasn't in the mood to make anything obscure, especially from X-2 because I suspect many of us who frequent this forum couldn't stand to beat the entire game.