Suggested by Destroyer Ansem is the Master of Darkness and a pretty tough opponent to take out for the count. That being said, Ultron has had numerous powered up modes over the years. This gives him access to a whole slew of abilities that most fighters can only dream of. With his fusion to Sigma, Ultron gained enough offensive firepower to completely blow Ansem away. The darkness just won’t be able to protect him this time and he won’t be able to hold out long enough to counter. Ultron wins.
How about Thor vs Ultron? Thor from Ragnorock/Infinity War/Beginning of End Game.
They did fight on the site a while back although Ultron was able to narrowly take the edge.
https://dreager1.com/2011/06/10/thor-vs-ultron/
I think Ansem (or Xehanort) should win this. Considering how you got TRON in Kingdom Hearts II, that could mean alot in this battle.
True he’s got a lot of skill and abilities but Ultron’s merged with Sigma and has had forms over the years that overpowered Thor, Hulk, and Sentry. It’s hard to see him going down in this fight as he can even overwhelm the darkness