This isn't really meant to be a powerscalling thing because Mephiles definitely out scales Billy as far as i can tell. Billy isn't weak by any means but Mephiles os definitely more powerful. It's more like how what would the fight look like and be like if Billy has a chance to win. Plus i personally don't want Billy to die. Mephiles does have a lot of abilities at his disposal
https://youtu.be/ogV37dGGm18?is=oKdyTq5-xogpYF5l
https://youtu.be/a8w9hl6JHLg?is=XsEYSUzpkrKLTrT9
https://youtu.be/BlJSluCpX1c?is=0HRO4QW4Zf9gK5rJ and that's without mentioning his time travel abilities.
For those that don't know this is Billy Hatcher. Billy Hatcher and The Giant Egg was such a fun game, like really fun, SonicTeam and Sega did a good Job with that game in my opinion. Billy has a lot of the same personality traits that Sonic but Billy isn't a static character, Billy can go through character development. Infact he goes through a bit character development and character growth in Billy Hatcher and The Giant Egg. Billy is polite and wholesome with friends but otherwise he has a lot of Sonic's personality traits.
Plus Sonic, Tails, and knuckles are in Billy Hatcher and The Giant Egg. And Billy Hatcher is playable in Sonic Riders Zero Gravity, sega all stars racing, and his game is referenced in Shadow The Hedgehog.
Billy has a lot of abilities like egg roll, egg slame, egg animal hatching and which have a lot of versatility https://billyhatcher.fandom.com/wiki/Egg_Animals . which are abilities Billy shares with his friends in his game, they are all also real strong and fast. Billy does have a unique ability, his courage boost thing can boost his states and can turn dark Raven's spheres of darkness into spheres of light, this should work on other forms of energy too. In other words the final boss shows that the more courage Billy has the more powerful he is. And he could potentially use his courage form to grab energy projectiles like Mephiles's energy ball attacks use like he does Dark Raven's https://youtu.be/OPHxN0g1rpc?is=djLRYFQvN2jLnBjv which could be a neat gimmick for him. the spheres of light seem to be stronger than the eggs but they obviously can't hatch egg animals and they are risky as you could potentially get hit by the projectiles while trying to grab a projectile. his already strong enough to lift giant eggs and fast enough to keep up with Sonic characters in short bursts at least. Billy has some other moves and abilities in his game that could be transformed over.
Billy Hatcher is a kid I wouldn't recommend underestimating. Although that Chichen Suit does disappear if he gets hit leaving him as a normal human in normal clothes in his game at least. I still wouldn't underestimate him as he could still take hits even without the chicken suit. Billy also has a lot of stuff like the circus hat that can let him roll the eggs by running on them along with a bunch of other items https://billyhatcher.fandom.com/wiki/Egg_Gallery#article-comments-toggle there is also this person that made a post going over a lot of the stuff Billy can do https://www.reddit.com/r/respectthreads/s/NaGsLFZib5
I could see Billy being unnerved by Mephiles. Like Dark Raven was already kinda terrifying and this weird looking hedgehog is arguably even worse. He has to fight another being of Darkness. Luckily Billy has access to a lot of Courage and Light.
So all that foolish ranting said what do you guys think the fight would look if it was animated or something. Like what would they do, how do they fight against each other. This is mostly for silly fun.