Very well done! How do i start? I gave you a fairly high rating in most of the categories, since i think your game is really well done. It seems quite polished, has nice pixel graphics (which i like most!) and the coin collecting sound is soooo satisfying. And this is good, since i like to have a good feeling when i play. This is where i think most that a game is worth to play. When i resonate with a good feel.
I want to emphasize the sprites of the protagonist and the coins. There very detailed and i judge this to very well chosen, since both are the main sprites for the game; while it's perfectly functional, that the background and ground is quite simple in comparison.
Off to your core idea: I like your concept regarding the theme a lot. Fake coins are quite innovative i think, in a game, where you are supposed to collect everything shiny ... and fast! :)
But, and here comes my personal criticism: Your great idea kills the gamefeel and fun for me. There is a timer and i should be fast, there is this nice and simple level, where i can imagine how i am going to fly through and have fun jumping and reacting. And then: I go a bit, then stop, then look hard: left spin? right spin? err ... get ....next....stop, look, think....avoid! ..jump ... then stop again...and look. This feels tensed. Playing it "right" is no fun at all. It's literally a platform crawl ...
So the next time i just ignored your fake coin idea. I rushed through, collected everything, had a nice mixture of good and bad coin collecting sounds, jumped like crazy, moved fast, back and forth and when i got ALL the coins, i smiled and felt well: THIS was so much fun. And i appreciate you for the same end screen with "next time avoid the fake coins", which i can easily disregard and add to myself: "yeah. or i don't and just have fun with your game". :-)
So what i want to say: Your game IS well made AND fun. Your fake coin idea is still promising and a very good one, i judge. I just ask myself, how could you implement it, without necessarily slowing the game down so much. I see, that you could memorize the fake coins and then make a speed run through your level. But then it would be a memory plattformer, not a "distinguish between fake and real" one.
I have one suggestion, a kind of compromise: Maybe DO make the fake coins easily recognizable. But only for a short time. Like every coin is the same, but the fake ones have a glitching animation for some seconds. So if you get near one and the coin glitches, you don't have to look hard, but you instantly know this one is fake and you can frantically try to avoid it. Maybe this would help to still be fast in playing and being in a fun flow, without stopping everytime. You could even stand still for some seconds in the beginning and trying to memorize the glitching ones. This would be easier, but since the glitching occurs from time to time and for some seconds a fake coin looks like a real one there would still be some kind of difficulty involved, challenging your memory: "Wait. this one was real, wasn't it? oh, glitch! (frantically hitting JUMP)" Maybe this idea doesn't really address the platform crawl problem in the end, but maybe it can be another impulse of making the game fun AND staying true to your concept.
This said, i want to be honest, and state, that i don't play speed running platformer games at all and i see, that speed running such games is often very much about memorizing, so ... well. :)