Ok, let's start: first of all, until now, this is the game that best fits the theme, IMHO. Also, the jump feels real good, so that's a plus. However, there's a good list of cons to the game. In no particular order:
- My antivirus recognized it as a virus yesterday, so I had to get it virus-checked before playing it today. Not your fault, probably Clickteam's, but still is a problem.
- The game defaults to a specific screen size and you can't change that. What's worse is that you can resize the window, which just makes the game screen float at the center kinda awkwardly. I have never used Clickteam Fusion, but I suppose that it's a low-level engine where you have to draw rects and sprites autonomously, so of course defaulting to a specific size is ok. However, it's not hard to implement a world coordinates system and use something to convert from world to screen based on the size of the window, and I'm sure Fusion has something to read current width and height of the window. If you really had to default to something, you would have been better off doing so at fullscreen, since games feel more fulfilling, IMHO, played fullscreen as opposed to windowed.
- The main mechanic is ok and I'm not good enough at the game to test that, but I fear that the moving threat could be broken when moving at extremely high speeds if you didn't cap that out.
- Some of the diamonds spawn extremely close to spikes (intersecting them) and the spike's hitbox is fit to the sprite. This is a problem game design-wisely, since you always want to let the player do small mistakes and not be punished for those if your game isn't supposed to be a rage game. I would have let the diamonds spawn in a way that their sprite doesn't intersect the spikes AND still have made the spike's hitbox smaller than the spikes themselves.
- The player floating midair is kinda awkward. You should have put a ground under them or at least moved it much further down.
- The game over screen is a tid-bit broken, as in it only shows the unit digit of your score (so if you scored 17 you'd get 7 in your game over screen). Probably that's due to the white rect being made to fit only one digit instead of being adaptive and the text being black, perfectly blending with the background.
- The replay and main menu texts in the game over screen have a strange behaviour. I don't know if that was intentional (and if so, why?), but you can only use them by clicking directly on the text. The common behaviour (which I think you implemented in the start button in the main menu) is to have an invisible rect around the text that can be clicked as a button. This is the point that confuses me the most.
- In the main menu you only have instructions for jumping (and, let me say, shift is a pretty strange choice. I would have gone with both spacebar and up arrow), which makes you think you can only do that and not move left or right. It's easy to realize that you can move left and right, but if you give control instructions, give them all.
- Also, you might want some music in the game screen, but I see that being a problem when time-restrained.
Sorry for the rant.