There are a lot of things but 3 that come to mind that are the most important, non-character related.
Remove/Alter TAC
The fact that you can get a safe tag without spending any meter, and build meter or get a damage boost at the same time and continue a combo (with a potential level 3 like gravity squeeze) with no serious potential consequence is just silly, it’s really just baffling that Capcom didn’t think that was OP. Honestly, it’s on par with X-Factor. It’s also a tactic that promotes scrub combos. When a TAC is countered, the opponent should actually be able to follow up the counter, it’s a fucking counter. It’s so stupid seeing the character who gets countered falling out of the sky while you can’t do anything. After a counter you should have the opprutunity to do a full combo. Sure you could make it so you just have to pay to TAC, but if you make it so there can be an actual counter, it’d happen far less frequently. The character who also gets the counter should also get the meter boost (or even better, take meter from the opponent) Maybe you could have the option of paying for it and not getting countered. The window to input the counter should also be a wider. Honestly, it shouldn’t be a reliable at tactic at all.
Fix X-Factor
Honestly, give it an off/on switch, that way people can play with it or not. A lot of times I play my friends in casuals without it, and it’s a lot more fun, the comebacks are far more rewarding. If you had to alter it, just nerf it across the board. Make level 2 and 3 much shorter (maybe about half the time) as well as a noticeable speed and power nerf. If a player is up 3 to 1, it should be virtually impossible for a comeback to occur. I hate watching streams and seeing that shit, honestly, I just roll my eyes. People say it’s not that big of a deal, and everyone has X-Factor, but when Dorm is level 2, and he puts out two floating bombs and then DHC’s into hailstorm, suddenly you have like no health and there’s nothing you can do about it. Shit like that is just silly, it’s obvious Capcom didn’t think it would be this game breaking.
Remove the DHC glitch
It’s not only OP but it discourages many characters from being played that don’t have the option.
Super Skrull (Really would love to hear more on fixing Skrull)
He’s my main character, I really like him, but I’m finally beginning to realize he blows. He’s not particularly GREAT at anything. His damage output is only great with resets which aren’t reliable or safe (for him), his assists blow, he’s not super mobile, he’s not very fast. Give him flight (along with a back air dash), I mean he’s fucking Super Skrull for christ sakes. That way he could do more damage with all his combos but you’d have to work for it. Dumb that you can’t even get to 600k from an elastic grab. Give him some type of projectile (I mean he’s fucking Super Skrull), I was thinking of something slow like a full screen kioken as a fire ball but with a lot of durability. It doesn’t have to be fantastic but something so he doesn’t get zoned out so easily. Buff his assist(s) give orbital grudge more hyper armor, and make tenderizer and stone smite do more damage. He really has some of the worst assists in the game. Also change the input for Rolling Hook, such a stupid input.
Hsien-Ko (For Killer Jiggs)
She really seems interesting, I really wanted to play her but she blows. She needs to be way faster, someone said 10%, but she needs to be like Chun fast. Give her a slight damage boost too, nothing crazy though, maybe like 15%. Make her projectile on a rotation, so you can actually use the dizzy. Make her air dash faster too. Hitboxes should be a little bigger. That’s pretty much it. Hyper Armor should also be longer on point, but not way longer.