The culmination of both of the above abilities, Unlimited Blade Works is the sum of all of Archer's magecraft. Unlimited Blade Works is a Reality Marble, meaning it allows its user to create a pocket dimension where the rules of the regular universe do not apply. In this case, Unlimited Blade Works allows Archer to create his own world, for a limited period of time, where he can use his Projection without limits. Normally, Projection requires that the user supply the magical energy required to bring a projected item into existence. Unlimited Blade Works circumvents that requirement, creating a world where Archer can materialize as many weapons as he wishes and wield them to great effect. The ability is his trump card of sorts, and is also what allows him to recreate extremely powerful weapons that would normally be beyond his ability. Because Archer has such a large repository of weapons stored away in his mind, he can create virtually any weapon (with some exceptions) once he is within his own world.
One day his ingame background will go here... maybe.