Worst choices for actors/actress in a superhero movie/show.

I'd say everyone in Fant4stic, but honestly that's more of a case of the wrong movie for the cast.
The actors in that one actually did a good job with what they had to work with. The problem is that they had to work with a stale turd of a script that makes Zack Snyder's DC movies look fun and exciting, and an otherwise incompetent production crew with a talent for making action-packed CGI scenes look boring and cheap.

Nicholas Cage as Johnny Blaze as also a poor choice. Man might be a big fan of the character, but he did not succeed in really bringing the character to life on the big screen.

Keanu Reeves as John Constantine. If you have to completely rewrite the character's backstory to suit the actor, you really should look into casting a different actor instead.

Jared Leto as the Joker. Guy really, really tries too hard to be the ultimage edgelord. Although that might also have been part of the script. Maybe he should have gone full juggalo and act more like a real clown instead.

Jesse Eisenerg as Lex Luthor. Absolutely fails to portray any of the calculated, pragmatic menace the character should carry.

Vinnie Jones as Juggernaut. Although, that probably was also due to a) bad scripting and b) the camera work somehow making him look smaller than his 6'2 instead of playing it up to make him look like the massive character he's supposed to be. If would have been funny if they'd gotten him to voice the character in Deadpool 2, but alas...

is Anakin Skywalker a super hero? if so i put a bid for Hayden Christensen in episode 2 & 3. i feel they should digitally delete and readd a new actor for him in those movies.

Ben Affleck playing Batman and Superman.
https://www.imdb.com/title/tt0427969/?ref_=nm_flmg_act_24
https://www.imdb.com/title/tt2975590/?ref_=nm_flmg_act_11

Anyone in Street Fighter Films? Mortal Kombat Films?

Stalone as Judge Dredd

Zazie Beetz as Domino in Deadpool 2. No clue why they decided to cast a black actress for no good reason. Domino in comics also has a backstory for her face tattoo (without spoiling, I'll say that skin color is a big factor) and in the movie, none of it was addressed at all which makes the casting choice even more baffling.