Scarecrow can get nasty if he gets close, becomes a slugfest that's not in star's favor. He also has that ducking advancing mid which is kinda hard to deal with outside of backdashing away or MB b3. Overall I think it's pretty even though.
Darkseid can be tough coz of the damage difference, you can punish his lasers if you're around halfscreen away with trait but it's strict. Trading with the lasers is also a no-go coz he does more damage and gets a knockdown so fullscreen zoning isn't ideal.
It's slightly in favor but nothing drastic.
Fate will win if you play it from fullscreen away, in a total zoning war he has the advantage coz all he to do is just fireball nonstop and star can't retaliate without trading or getting stuffed especially if he has trait on.
you have to be a bit closer to win, midscreen-ish where his fireball whiffs is the sweet spot. On wakeup f3 is very good against him coz it checks glyph free so you get the momentum if you're close.
I don't see how hellboy is 7-3 tbh but I haven't played against him enough to judge the MU.
If it's the leap then you need to do more close stardusts or ume b2s, and if he cancels it it's generally a free db3.
for his armor trait i generally use up full trait or throw out stardusts in his way to slow him down, you can also just bf2 all over the place and make him chase you till it runs out.
Supergirl is still her worst MU imo, you can't play footsies against her coz it's too risky and star gets minimal damage where supergirl can get a full combo if anything hits.
her fullscreen options also shut down starfire be it air lasers, ground lasers or teleports. She also has the initiative on wakeup as star's wakeups blow against anything from the air which supergirl can do easily with airdash mixups or simply f3 shenanigans.