As a co-founding member of the superhero team Teen Titans, Starfire is one of the strongest young DC superheroines. She's one of the heroes who successfully manages to combine not only in leading her team but also in fighting crime and having a personal life since her boyfriend is the superhero Nightwing.
Starfire is a kind-hearted person but it's not a good idea to cross her since she's very powerful and has brought down many enemies during her existence in the comics. If Starfire crossed over to the Marvel universe, she'd be able to defeat some of its villains but others would prove too much even for her.
10 Could Defeat: Loki
The duel between Loki and Starfire would certainly be interesting since both of them have a fair share of useful tricks and powers up their sleeves.
But when physical strength is concerned, Starfire does better than Loki. Yes, he can use his magic against her, but Loki is primarily a trickster and Starfire is smart enough not to be fooled by him. So in this case, strength wins over magic.
9 Would Lose: Apocalypse
Apocalypse may not have looked like much of a threat in the live-action film X-Men: Apocalypse, but in the comics, he's a force to be reckoned with. Apocalypse has a list of powers much longer than Starfire and he also happens to be one of the strongest mutants ever.
He's as close to immortal as possible, has the power of telekinesis, can create force fields, send out energy blasts, and much more. Even Starfire's considerable strength and her star bolts would be no match for the villain.
8 Could Defeat: Red Skull
Starfire might have a hard time defeating the whole of Hydra but taking on only Red Skull himself wouldn't be such a challenge for her. Red Skull is good enough at hand-to-hand combat and he's able to trick his opponents, but he's nowhere as strong as Starfire who's superior to him at almost every level, maybe except her combat experience.
Still, even with all the knowledge accumulated, Red Skull wouldn't be able to take Starfire down all on his own.
7 Would Lose: Thanos
Everyone's favorite Mad Titan Thanos is one of the strongest villains in the whole Marvel universe, and it's safe to assume that defeating Starfire would be as easy for him as swatting a fly, and that's without the Infinity Gauntlet.
Thanos is easily able to defeat a whole army of people going against him and as his epic showdown with the Avengers in the film Avengers: Infinity War demonstrated, one hero, no matter how strong, isn't enough.
6 Could Defeat: Black Cat
Black Cat is one of the more sympathetic Marvel villains who moves on the thin line between being an antihero and being a villain. And she's also no match for Starfire.
Black Cat is a human who's agile and fast and has the power of bringing other people bad luck (in some versions of the comics, anyway). Starfire is a super-strong alien who shoots energy blasts out of her hands, so the fight would be over almost before it could start.
5 Would Lose: Dormammu
The longer someone's list of powers is, the greater the chance they would defeat Starfire. Dormammu is no exception. Both of them might have their origin outside of Earth, but that's where the similarities end.
Dormammu is a virtually immortal cosmic entity who has many powers, such as matter transmutation, interdimensional teleportation, telepath, element control, and he can also create his army of demons who would tire Starfire out long before she could get to Dormammu.
4 Could Defeat: Kingpin
Kingpin is strong enough, for a non-powered human anyway, but his greatest power lies in his criminal underworld, not in his body. Daredevil had been able to defeat him and since Starfire is stronger than Daredevil, she'd also bring Fisk down.
He might be able to get in a good punch or two, but if Starfire decided to blast him into oblivion, there's very little he could do. As long as she catches him alone, she should be fine.
3 Would Lose: Galactus
Generally speaking, space villains would often prove too much for Starfire, Galactus included. His name Devourer of the Worlds suggests that this character is no D-list villain.
In fact, he's sometimes considered the most powerful creature in the universe. Starfire is a powerful character, but Galactus is a being with godlike strength, stamina, and speed, he's invulnerable, can create force fields and other choices of defense and attack he'd use against Starfire to defeat her.
2 Could Defeat: Bullseye
Bullseye can supposedly lift twice as much as his body weight, which is impressive, but he's still not as strong as Starfire, not by a long shot. He prefers to take his victims down from a distance and has trained to become an effective marksman who rarely ever misses.
But even if he managed to hurt Starfire, who's faster than him, she could get closer to him fast and knock him down.
1 Would Lose: Mephisto
Fighting a villain named Mephisto is never a good idea, and if Starfire crossed his way, she would soon find this out. Mephisto wields mystical energy which he can use for blasting force against his opponents (similarly to Starfire, except stronger).
He can cast illusions, trap living beings in his realm, and do an even larger number of tricks that would make the fight between him and Starfire very one-sided.