Tomura Shigaraki Analysis
Main Win Conditions
Tomura's win condition is to use his superior stamina to try and outlast Danny. This is possible, as Tomura starts out with a hefty power advantage, and while he can't actually deal harm to Danny, he still can "damage" his body while it's in a physical form (which it almost always is). This will force Danny to reform himself and thus waste energy doing so, and this can also be accomplished with Decay as well.
Supportive Advantages
Search will allow Tomura to know Danny's location so sneak attacks using invisibility and such are out. Tomura's rage power and quirks that allow him to amp himself will help him counter Danny's amps once the later reaches his level. Reflect would also allow him to send Danny's energy attacks back at him and since those carry ectoplasmic energy, they can actually cause Danny harm.
Tomura's supernatural willpower and resistance to possession will allow him to resist Danny's attempt to Overshadow him but only for a time, as Danny's possession has been shown to be layered and his own supernatural willpower can counter. Wings and Air Walk would also allow him to keep up with Danny in air combat.
Finally Tomura's fear inducement would be an annoyance but I wouldn't bet on it being a deciding factor as Danny has resistance to mind based stuff, and even though it's Tomura's presence that's causing it, it's still effecting the targets mind. Given Danny's own supernatural willpower and the fact that he's already a ghost, the visions of death shouldn't be a heavy issue
Danny Phantom Analysis
Main Win Conditions
Danny's main win conditions are holding out until his Reactive Evolution buffs him to Tomura's level of power and using his energy attacks that work on a molecular level to overpower Tomura's level of regeneration. Given how fast Danny's statistics increased against the Fright Knight (who is 6-C+) it wont take much time for Danny to reach Tomura (who is 7-A+). The real issue is getting a solid hit on Tomura do to his Reflect and Scatter quirk.
Another win condition is Danny Overshadowing him. While Tomura has supernatural willpower/resistance to possession, Danny has his own supernatural willpower and layered possession, plus his reactive evolution makes his abilities more effective as shown when him and Sidney had a long struggle during his first attemp at Overshadowing Danny but during the second attemp, Danny reversed it in seconds without issue.
Supportive Advantages
Ghost Physiology gives Danny several good abilities such as intangibility and body control which can help him avoid Tomura's attacks (though Danny doesn't spam intangibility), he has several ways to amp so once he's on Tomura's level, he can counter the later's amps with his own and it should be noted that Danny's amp ectoplasmic energy amp has allowed him to tare through people comparable to himself.
Danny has his own ways to block and reflect ranged attacks with his ecto shields which can stop attacks well above Danny's level without issue. His regeneration will also allow him to hold out for some time but it's stamina based sto the moment he gets tired/loses enough energy, he'll revert back into his human form and can be killed.
My Vote
It's an interesting fight overall in my opinion, and I'm going say Danny pulls out win in the end.
My Reasons
Tomura's arsenal gives him a shot at taking down Danny, and he has the stamina to hold out longer. Danny's overconfidence can also be factored in but Danny's versatility thanks to his Ghost Physiology makes him capable of surviving the short time needed to get the buff from his Reactive Evolution and get serious.
Danny's also not lacking in the stamina department so he wont go down extremely fast. He may not spam intangibility but body control is something he does a lot, and while Tomura's Reflect makes it hard for Danny to vaporize him on a molecular level. I see Danny landing a possession that will overcome Tomura's resistance.
It should also be noted that multiple ghosts can overshadow a single entity so All For One being inside Tomura as well wouldn't hinder Danny's possession, plus possession in Danny Phantom allows ghosts to interact with the users subconscious/spirit so he might even be able to blast All For One's visage.
Either way, I think Danny can pull off a win faster than Tomura.
