The year is 2217 and the mutant human war has taken a turn for the worse, the humans in a do or die attempt have built a robotic super soldier, its name was Bastion, and they set it loose with only one command “wipe out all mutants from the planet earth”. The problem is that it’s AI turned on the humans themselves and determined that to kill all mutants you must kill all humans from which they came, it used the advanced technology and stolen genetic mutation powers to leap back in time to the year 500 BC, it crashed into the plants surface sustaining heavy damage and putting itself into a hyper-repair cycle to try and restore its systems; time pasted as it does and soon the robotic body found itself functional but without a new power source, the humans of the time feared at and trapped it in a large cavern.
The year is now January 2000 and archaeologists have discovered this hidden tomb for the robotic life-form, the removed it from its resting place and used the technology of the day to recharge its power cells; it awoke and killed all the humans in the labs and building before vanished from existence once more.
Once more time passed without any sound from the robotic life-form until it struck, the date was the 20th of December 2012 and unlike every other day today was going to go down in history as the day Bastion returned and turned to world upside down; his first strike was like a scalpel, he had built smaller copies of himself called sentinels and sent them out into the world to track and kill the most prominent among the mutants of that time, the X-men.