Okay let's talk here.
For starters, this is a really fun and polished platformer! But it definitely can be way better. It is currently in "early access/late beta" stage in my opinion.
PERFORMANCE
Game runs silky smooth at my relatively clunky computer. Out of curiosity I checked and it runs in resolutions as low as 1024x768. Aside from camera freakouts in enclosed spaces (I recommend that in small spaces, walls should simply become transparent) I never got any glitches.
Also you can't enter fullscreen, which is weird.
CONTROLS AND MECHANICS
For starters, the game doesn't have a drop shadow. Look at every 3D Mario game ever released - Mario has a clear shadow that is *directly 180 degrees below him*. Always. That isn't there for aesthetics like your pretty accurate shadows - it's a GAME HINT. This makes it much easier to judge jumps that go directly forwards into depth, because this allows you to instantly tell exactly above what ground Mario is. Some Mario games like Odyssey go even further - in Odyssey, literally all object shadows in the game have just perfect drop shadows - but you can probably get away with having drop shadow for Mario as an optional toggle.
Coinboxes should get a drop shadow too, currently something as simple as hitting a coinbox above you can take several tries.In fact, I think moving platforms and so on should also get drop shadows.
Momentum - Mario currently has way too much momentum, this isn't Sonic. Mario should start on a dime and stop on a dime - accelerate fast, decelerate fast. This would allow for good and precise controls. This also affects how the walking feels - it doesn't feel the best right now. Mario kinda controlled like that in Mario 64... but we moved a long way from Mario 64.
Longjumps - longjumps are awful. It's so easy to accidentally make a backflip when you want to make a longjump (at least on keyboard) - this should be tweaked. This is because it's actually way too easy to make a backflip - in my book, you should only be able to make a backflip if you're completely standing still. Similarly, I'm not sure if you can do a longjump before you fully accelerate - if not, there should be some kind of a cue (a puff of smoke? a sound cue? both?) to indicate you're now in "longjump capable mode". Speaking of, some kind of tutorial of your movement wouldn't be a terrible idea. You kinda get tiny bits of info in CBM but it's too little IMO.
Dive - the game doesn't have a dive. The game badly needs a dive. I think it could be as simple as pressing Jump in midair.
Springs - springs are currently terrible. Springs should make it easy for you to 'charge' a jump by holding Jump button, and then release you at full speed. Currently they're like, a floor that makes you jump higher. Like, no, that feels bad.
Attack - you have absolutely no attack whatsoever. I genuinely don't understand that, every 3D Mario game that allowed you to freely roam environments had some kind of attack - punches and kicks in 64, FLUDD in Sunshine, Spin in Galaxy, and hat toss in Odyssey. It just makes sense in a 3D space, especially since you can unlock characters known for their offensive capabilities - I'm supposed to believe characters from Fire Emblem or Genshin Impact can't make an attack?
Speaking of combat, enemy hitboxes are wonky. It is super easy to get stunlocked when fighting a Charging Chuck, and really hard to actually defeat it. Also there is no reward for doing this tough challenge - enemies should drop coins IMO, that would be great since coins are central to the main mechanic of unlocking characters. Also, you don't seem to have mercy invincibility after taking a hit (or it's way too short). Also, Mushroom is a very rare item but only restores 1HP. Why? If it's so rare, it should bring you to full health. Or maybe you can replace it with spinning hearts from 64 that allow you to endlessly refill your heart when you visit them.
Star animation - in most Mario games, star grabbing animation freezes everything. Here, it only freezes Mario - what happened to me in Sweet Donut Plains is that I grabbed the Charging Chuck's star with 1 HP, and then I could simply watch as Chuck was running straight into Mario during his victory animation, waiting to murder me the frame I unfreeze.
LEVEL DESIGN:
Level design is currently way too hard. I don't mind a hard platformer, but this has issues. First of all - not everything is too hard. Most things are at normal difficulty, until you suddenly toss an insane challenge at the player out of the blue. Which leads me to believe this isn't intentional, but a balancing issue and lack of playtesting.
Example - propeller hat challenge in Color Block Meadow. You are introduced to the propeller hat. Your first jump is a trick jump where you have to propel off a walljump - and some people won't even know what the item does yet! Then you have to ascend a tower. You have to figure out a puzzle that you can stand on a tree - not obvious, you can't stand on trees in most games, and you can only do that because you have a higher jump now which player hasn't learned fully yet - and then you have to figure out you have to backflip into a propeller, and then you have to jump all around the tower, and then finally top it off with another walljump-into-propeller...
... just to get your first ever star with a Propeller. Hell, because game is nonlinear, this could be someone's *first star in the game*. If that happens, some people might literally ragequit the game right here, if you're really bad at platformers I can easily see this star taking you 20-30 minutes (it took me like 10 and I have like 0 experience with 3D platformers, but I might've gotten lucky). I think this challenge should be replaced with some way easier introduction to Propeller Hat, and that this original challenge should be copypasted to some level in the midgame instead. Oh, and there is literally no reason why this entire thing should be on a precarious tiny island that you can easily fall off from.
Similarly, the Donut Block star in Sweet Donut Plains is kinda insane? Like, the issue comes at the end - very close to the summit, with no warning, you have a jump that is too high for you to simply jump it (I couldn't) so I'm assuming you have to backflip it? First of all - you have to guess to do that with no warning. Second - even if you know to do that after you die once (bad design, this isn't Kaizo!), trying to fully rotate, crouch and backflip on a platform that is FALLING is absurd. This jump is just bad. I recommend replacing final Donut Block with a solid platform. It's currently completely insane.
Like the issue is that you test players on mechanics *before* you introduce them, which results in a wonky difficulty curve. Not every of your players will be familiar with every gimmick from every Mario game. Instead, a better idea might be to follow the 4-step level design approach -
Minor things - the gap in the middle of Color Block Meadow that you're supposed to longjump for coins is way too big. It's super easy to fall in the pit in die. Obviously that's bad in a tutorial stage, lol. Especially since longjumping sucks so hard.
Because of Mario's insane momentum, it's really easy to fall off platforms. This is especially apparent in Colorful Jumping or whatever it's called star in CBM. I can guarantee you - it's never fun to overshoot a platform because of momentum.
Oh and a minor thing - in CBM, you can get the star for climbing the tower hill - instead of finding the key coin and warping up with a key warp block, you can simply stand on the fence below the moving platforms, jump onto the coinblock, jump onto the tree, and backflip from a tree onto the platform. That's actually how I got this star first time and was surprised that the key warp took you there, I thought mine was the intended way. I don't think that is something to be fixed, just wanted to let you guys know it's possible as a curiosity - maybe add an achievement for it or something.
QUALITY OF LIFE:
I will openly admit, I hate the gacha crap idea. First of all, the unlock calendar is simply annoying. It doesn't make me want to return to the game - it makes me want to never play this game again. I just spent 200 gold on a character I don't like at all, which feels like a complete waste. And now you ask me to spend 190 so I can do it again? Eff you, dudes.
I can guarantee you I will NOT memorize the summon calendar and return when a franchise I like is "on" - do you really think I will *arrange my day schedule* after a Mario fangame? Not that it would help any, since I don't like any of these franchises. Like, literally, I don't give a shit about a single one of these series. Even the extended list that is not on the calendar doesn't interest me at all maybe aside from Black Rock Shooter - but if you think I'm going to spend literal months grinding coins in Color Block Meadow over and over (only stage I've seen that is good for coin grinding), with like a 100 draws to maybe one day get the BRS girl (because it's like, one in a hundred or something chance) you gotta be nuts.
Like the franchise choice raises my eyebrow. Like, you have Mario but I can't even get Peach, Daisy or Rosalina? No Full Metal Alchemist or My Hero Academia? Or Fairy Tail or One Piece or idk, anything? Or maybe they're in the game. I wouldn't know, because characters are hidden before you unlock them. That demotivates me from even trying. Gacha games have their rosters publicly known, so people will be happy to get a hero they wanted.
Like the characters aren't even useful. They don't have different stats or special abilities like in actual gacha games - they don't even have story bios. I can guarantee you that myself, once I unlocked a single character I want, I wouldn't care afterwards. I don't even know what characters I *can* unlock, why should I care? In fact they hinder you - I tried out the character I disliked from Touhou and I had a really hard time making jumps, I literally couldn't even jump into the portrait several times - there is something wrong between the hitbox and then model, I'm not sure what exactly. I could jump into it eventually, but I think my character was halfway phasing into the wall when the hitbox was aligned correctly.
Personally, I prefer if you had a choice when making a new save file - you can either enable Gacha mode, which will drastically lower the cost of summoning - OR a Buy mode to allow player to pick a mode where they summon whoever they want specifically out of a clear list, out of any game, but for a higher price than normal, and price doesn't get lower. I would way prefer that.
Speaking of save files, save file selection should show you percentage completion of levels, number of coins, and percentage completion of character unlocked.
Also I have no idea what is the point of Daily Challenges. It seems they only make sense as a 'postgame' since you can't even find most of these enemies unless you already unlocked a bunch of the levels. But I can guarantee you, nobody will log in into a 3D platformer just to grind a Daily Challenge to maybe unlock a new character. Like that's not gonna happen. Gacha games exist because they regularly produce new content.
And it's not like current content is well suited to grinding! Even though coins are an extremely important collectible, there's barely any coins in the game! How am I supposed to get 200 coins and so on? I 100%ed Color Block Meadow and that wasn't enough to unlock my first character, absurd! And out of early set of stages, CBM seems to be the best stage for grinding coins, which is gonna get old FAST. And grinding coins is boring, most coins are in coinboxes or spinning rings - and the way to collect a spinning ring is to literally stand in place as coins come towards you. Snooze.
Level design should REWARD player with fat stacks of coins for accomplishing objectives, and maybe you should make some kind of minigames that also reward coins. Look to Mario games - Super Mario Odyssey does reward you with huge piles of coins for taking side paths, and as for minigames, you can look at games like 3D World, with it's levels where you have to take on series of enemies, or its Captain Toad levels. So some kind of endless enemy survival would be nice. Bonus points since it'd also help with grinding out the Daily Challenges.
Finally - you can't see the star names once you complete them, pause menu only tells you completion percentage. I have no idea why is that, every Mario game lets you see name of your objectives.
Don't get me wrong - I think it's admirable what you guys got here so far, and it's a great foundation. But it needs work.