Joker is a great Batman villlain who can beat Batman any day of the week. Of course there is a big difference between Batman and Ultron. Ultron is super smart and has resources. He’s got hundreds of bodies to back him up. Joker can only rely on himsell. Plus Ultron has raw power. Ultron wins.
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Most of the time, Ultron should take this. But if The Joker can outsmart him, then the latter has a chance.
Joker would definitely need to find a way to get in close and deactivate Ultron or something. With his trickery it’s definitely always an option