Nice art style and overall very pleasant to look at. The constant sprite tearing was a bit annoying to look at but obviously nothing major. But should be easy enough to fix with a quick google. Can't remember off the top of my head how to fix it as I don't often work with tile maps on Unity. And was the background parallax the completely opposite of what it should be like? Wasn't it moving faster than the foreground? Something about it looked off to me.

There were also few outliers that didn't lit the overall pixelated look. The collectables and the bullets didn't quite fit. The bullets were also a bit too small and slow in my opinion. They were actually so slow that when you pick up enough speed, you can't even shoot the enemies anymore as you run past your bullets. Might also want to turn on the "scale canvas size with screen size" option on the canvas so the UI elements aren't that huge when not playing full screen (or when playing on a smaller screen).

Might be just me but I had difficulties figuring out the state which the lighter platforms were. Their on/off states weren't distinguishable enough in my opinion. I don't think the game would even need two different styles of blocks as they'd already be distinguished enough by their phase. But I think quite a common trick with these kinds of systems is to have an additionally different style for off blocks on top of just dimming them. Mario Maker and Celeste come time mind as examples that tackle this issue well.

A quick game focused on running against time really would need a quick restart and ability to skip the cutscene on the end. It's no fun trying to improve your time when there are constant hurdles and delays put in front of you. The whole level design also didn't quite feel perfect for speed running. One of the early enemies was perfectly synced to make you either have to wait for it, get hit or skip the collectible (and jumping over it was very inconsistent too). And of you play flawlessly to the end, the final two enemies are impossible to shoot as you have so much speed. Doesn't feel great.

The audio work was pretty good. The music seemed a bit too cheery and chill to fit the game though. And there were quit a lot of actions which were missing sound effects like jump landing etc which made it feel more desolate and made the existing sound effects get more repetitive.

Nice art style but I don't know why the son would be shooting clones of his dad?

This was just a delightful little game! It's a nice twist on the overdone "runner" concept, and all 3 of the mechanics you've created (running, swapping, gun) tie in well with one another. My only suggestions are little things, like making it more clear when the player is hit, or having indicators when the player is speeding up (speed up the music or make a super fast running animation for the character), but other than that, it's great! The colors you've chosen for your pallete are great as well. All in all, a fun micro speedrunning game!