Hmm...
Well, looks like you're doing good so far with your project.
I see you're using Open Surge as the engine. Not a bad choice.
I was having additional thoughts on others that would've done well, comparably to Taxman's Retro Engine, such as the Orbinaut Framework, which has been upgraded to 2 lately, and the Harmony Framework, made by Darkn, used in Sonic Aural(there's a demo up for download to try, if you want to.), another fangame I've seen.
You know, I think Retro Engine should be more used by people to develop more new games, alongside more new 2D Sonic games, but so far, that engine's not available for public use. Sure hope Taxman can make it so sometime soon. People will want to use it.
Back to the two frameworks...
So far, both of 'em did very good at utilizing the 2D gameplay formulas past Sonic games have before, aside from small differences between them.
Sonic Worlds, another framework usable for Clickteam's Fusion engine, has been used for Freedom Planet, from what I've read, to maintain the Sonic 3 formula staples(which weren't used since Sonic 3 & Knuckles, true thing), with small changes during its conversion to its own indie game, has been also a fine choice, but I get the whole of Clickteam's engine hasn't been updated and optimized to handle far more larger level maps, at least, past the yet-to-be reached limit after its raised from MMF2's size limit of 32,767.
A different fork of it, Simple Sonic Worlds, has been used for another Sonic fangame that surely could be a potential prequel adventure to Sonic 1, Sonic Overture '95. That game really gives thoughts and insights on how Sonic and Robotnik first became sworn enemies, and how it keeps in line with what Sonic 1's Japanese manual's storyline describes on how Sonic always thwarted his world domination schemes since they've truly met. I don't ever count Sonic Origins as the definitive tale. Its only a compilation that adds in animated scenes for each game.
Those are all neat frameworks for making Sonic inspired levels, but their differences stand them out from each other, as well as their efficiencies.
If you're up to trying them out, you can download the Orbinaut Framework(requires Gamemaker to use) and the Sonic Worlds framework and its aforementioned fork(requires Clickteam Fusion 2.5 to use). Harmony Framework, though, has just been made downloadable, but right now, its at 0.91. Its usuable and downlodable, but close to being complete. You can still keep Open Surge, though.
Not all bosses have to have phases. I've been content with bosses, past and present, that were damage sponges, but I've been through others that changes their attack patterns, not doing multiple phases, that's for final and true final bosses, after taking enough hits to make them less tedious. Just a matter of being a bit inventive with the patterns while still making them endure great damage.
Oh, my 5 best Sonic games? Well...
1 - Sonic the Hedgehog 3: Easily the overall best Sonic game! A great adventure spanning over more than 10 Zones, packing more larger Zones, seamless Acts without needing fade-outs to the next, new Act 2 themes that remixes the Act 1 theme to make each Zone more exciting and distinctive, in-game storytelling to convey the action better, better variety of bosses, including the addition mini-bosses in the end of each Zone's 1st Act, which I REALLY love, and, Knuckles, who's been a worthy addition to the series. My best Sonic game yet, even split into both halves!
2 - Sonic Mania: That game is a far more greater definition of a continuation of Sonic's 2D platforming adventures! Retouches many past Zones to give it the aesthetics of an actual Sonic game on the Sega Saturn, one that actually continues from the formula after Sonic the Hedgehog 3 as a whole. And, I enjoyed the original Zones, too. Really contributes to Sonic's anniversary. And the "Sonic Mania Plus" update brings back Mighty and Ray after being long absent in the series!
3 - Sonic Rivals: That game puts the emphasis of speed to reinforce the competition aesthetics and aspects by pitting two rivals against each other for the goal! Silver's proper introduction helps, too. Really loved it!
4 - Sonic Generations: Easily one of my best 3D Sonic games that celebrates Sonic's birthday, disrupted by the time-tearing monster, Time Eater, spanning visually overhauled stages from the past and the near-present, utilizing both of Sonic's selves to travel through each stage's different perspectives.
5 - Sonic Unleashed: Best one! That game introduced key additions, such as the Boost in 3D games, the Quick Step, Sonic Drift, and using his Werehog form at night to fend off monstrous minions, in a global-wide adventure to put the planet back together after Eggman broke it apart to awaken Dark Gaia, and the first to use the Hedgehog Engine and used in later games since!
