Big Chill. Rex chases after Ben and both are confronted by Caesar, who explains the creature's origin, saying that he created the creature (named "Alpha") as a means of manufacturing nanites that could adapt for any scientific need, but it became rogue as it developed sentience and tried to possess human bodies due to its inability to hold a physical form within a machine, forcing Caesar to banish it to another dimension. However, Ben deduces that Caesar actually sent Alpha into the Null Void, a prison dimension for intergalactic criminals that the Plumbers capture, allowing Alpha to obtain a physical form within a cyborg alien and find its way back to Manhattan. Alpha invades to absorb EVOs for their nanites, hoping to gain control of Rex's as it knows he holds the key to it obtaining perfection: the Omega Nanite. Back at base, Ben and Rex explain each other's origins, as White Knight reveals that Alpha has gone to the Bug Jar, a quarantined city full of EVOs for it to absorb. Rex, White Knight, and Ben arrive, only to find themselves against the nearly invincible Alpha, which begins to attack to take control of Rex's Omega Nanite. Ben fights as XLR8 and Four Arms. During the battle, Ben gains the form of Shocksquatch (who would later be seen in Ben 10: Omniverse) but then temporarily loses his powers when Alpha copies the Ultimatrix and takes on Nanite powered versions of Heatblast, Four Arms, and Humungousaur. After a tough battle, Rex is able to disable Alpha's imitation Ultimatrix powers, but is ensnared and robbed of his Omega Nanite, leading Alpha to transform into a colossal being calling itself Alpha-Omega; the beginning and the end. As the now nearly unstoppable Alpha-Omega rampages, Rex has doubts about himself now that most of his builds are gone. Ben however comes up with a plan, and transforms into Upgrade and merges with Rex, enhancing any machines that Rex generates. The duo then take on the Alpha-Omega, weakening it enough for Rex to finally condense Alpha into a sphere of matter that weighs several tons. As Alpha was being condensed, Caesar appears and extracts the Omega Nanite. Attempting to dispose of Alpha, Caesar then opens a rift for Ben, who changes into Upchuck and devours the compacted Alpha as he heads back to his world. Rex returns to base one last time to find that