Short answers, pulled from the story.
Ultimate Marvel vs. Capcom 3 is a crossover fighting game developed by Capcom in collaboration with Eighting, released for PlayStation 3 and Xbox 360 on the 15th of November 2011, in North America. It is an updated standalone version of Marvel vs. Capcom 3: Fate of Two Worlds, featuring 48 playable characters from Capcom video game franchises and Marvel Comics.
The 2011 Tohoku earthquake and tsunami disrupted the development schedule for downloadable content planned for Marvel vs. Capcom 3: Fate of Two Worlds, compounded by staff health issues. Producer Ryota Niitsuma decided to release the proposed DLC alongside rebalanced gameplay and new content as a separate discounted retail title rather than individual add-ons.
Capcom announced on the 13th of December 2013, that the game and its DLC would be pulled from online platforms due to the apparent expiration of its licensing contracts with Marvel Comics. The underlying cause was The Walt Disney Company, which acquired Marvel in 2009, choosing not to renew Capcom's license in order to use Marvel characters in its own Disney Infinity series.
The game sold approximately 600,000 units worldwide for PlayStation 3 and Xbox 360 in its first two months of release. By March 2015 it had reached 1.20 million units on those two platforms, and across PlayStation 3, Xbox 360, PlayStation 4, PC, and Xbox One it has sold 3 million units total.
Twelve new playable characters joined the original 36 from Fate of Two Worlds. Marvel additions included Rocket Raccoon and Nova, chosen in part to cross-promote upcoming Marvel products. Capcom additions included Firebrand, selected because Capcom wanted a monster-type character capable of fighting while airborne.
The game returned digitally on the 3rd of December 2016, for PlayStation 4, timed to coincide with the announcement of Marvel vs. Capcom: Infinite. Xbox One and Windows versions followed on the 7th of March 2017. The re-releases ran at 1080p and 60 frames per second and included all previously released DLC plus a new gallery mode with artwork from Marvel vs. Capcom: Official Complete Works.