A few suggestions
1) adjust walk animation collision bounds
2) make the transition region on the edge of frames smaller
3) make the coins more even not clumped
4) there is a slight delay as the monkey hits the coin, which feels weird gameplay wise

I think thats mostly it in terms of things that need improvement. Obviously this game is way to simple, but I feel like this is one of your first games so I won't criticize effort/work put in. Keep working and get better.

needs more, i got to the end and nothing happened, just a dead end. definitely some music would be good. The falling seemed very slow, and the jumping too. I liked the fade, so half a star for that.

It's awful, but it's awful in all the right ways.
The monkey seems to collide with the coins temporarily until he collects them. He's also very sticky and seems to cling to every wall. Perhaps this is simply monkey behavior and he enjoys clinging to walls. The end of the level, while the jingle it plays is endearing, it provides little in the way of climax since nothing happens to the screen albeit it could be a statement on the futility of the monkeys life and the entire goal was in his head. It did however trigger a laugh from me so good work on that.
Regardless, this is clearly some kind of coding test so good luck in your future endeavors.

It's a good idea for an old-school style platformer, but the controls are sticky and it ends abruptly.
For the controls, when you jump it just kinda sticks mid-air if you hit a platform before total height is reached. If it was a necessary, you could literally stick & jump from wall to wall to get down into a ditch, so maybe just add levels where that's important?
And when you get to 3700 points, the end of the third stage I believe, music plays and then nothing happens so I'm guessing its the end? It should be lengthened though.
Also, I was trying to listen to music while playing so a mute button would be a nice addition.

That's it? Just a (mini) monkey who collects coins? No enemies, portals, anything?