Ultron Sigma

Ultron Sigma is the merged form of Ultron and Sigma and the main antagonist of Marvel vs. Capcom: Infinite. He is voiced by Jim Meskimen and Chris Tergliafera, the voice actors for Ultron and Sigma, respectively. His "voice" is that of both Ultron and Sigma's voices overlapping each other, owing to his being fused from the two characters. As with previous Megaman X titles, Ultron Sigma also evolves into a final form in the final battle, known as Ultron Omega .

History
Ultron Sigma challenges Thor, alongside Rad Spencer for the throne of Asgard (renamed Xgard under Ultron Sigma's rule), with Ultron Sigma declaring arrogantly that their will is law and thus they will destroy them. Regardless of whether the player wins or loses, however, the demo will end the same way once Ultron Sigma's health is whittled down to a third: Ultron Sigma will disable Spencer and Thor with a chest blast and a beam saber slash, respectively, and then decries them as pitiful before asking if they even realize how powerless they truly were. He then steps on Thor's hand just as he reached for Mjolnir, and declared that he is not to weep for the Asgardians due to their achieving perfection under his rule. He then cruelly tells Thor that he'll soon "be their prince once more" before charging up an energy blast on his arm to transform him into a Xgardian. Before he could land the final blow, however, Ultron Sigma was shot in the back. Unphased by the gunshot, Ultron Sigma, realizing that Chris Redfield was behind him and shot him, calmly asks him if the commander had something to add in terms of great insight. Chris, however, merely tells him that he's going down. Ultron Sigma expresses some mock-disappointment in that all he had to offer was a "banal cliché" before declaring it to be fitting as final words from him. Ultron Sigma then levitates up and proceeds to charge up an attack above him before firing at Chris Redfield. However, Captain America deflects the blast with his shield, while Strider Hiryu retrieves Thor and teleports behind, with Ultron Sigma noticing just as it happens. The heroes then escape via Doctor Strange's portal, although Ultron Sigma nonetheless is glad over the overall turn of events despite losing his quarry.

Powers and Abilities
After a fusion between Ultron and Sigma, and the Infinity Stones (the Reality and Space Stones) they held, Ultron Sigma obtained both of their powers.

With power over Space and Reality, Ultron Sigma is nigh omnipotent

Trivia

 * Ultron Sigma is the second original antagonist for the Marvel vs. Capcom series, behind Abyss, but it is the first fusion of playable characters in the series.
 * This isn't the first time Ultron has fused with another character; For example, recently, in the comics, Ultron has fused with his creator Hank Pym.
 * Ultron Sigma can be considered to be a counterpart to Dark Kahn from Mortal Kombat vs. DC Universe, a fusion of two supervillains from two alternate universes and two different companies. (Note: Midway Games, the original developer for the Mortal Kombat series of games, was bought out by Warner Bros., which also owns DC Comics, and was rebranded as NetherRealm Studios.)
 * His leitmotif incorporates elements from Sigma's battle theme from Mega Man X2/X6 as well as the following tracks, "Heroes/Avengers Unite" from Avengers: Age of Ultron's original soundtrack.