I really love this.
I will start with my gripes first.
-I felt the overall level design was bland most of the time. There were many open spaces which felt needlessly big. It would have been better to just make them tighter and decorate them more interestingly. Your world begs for interesting environments. The smiling bump was a great touch; you need the whole world to be bristling with more interesting stuff like that!
-The platforming can be strange at times. If you approach a solid (platform) object from the sides (even for a single pixel) you just pass through it and immediately start falling through it. This was most noticeable on the cactus. I jumped on his head, walked a bit to the left, passed through his arm on the left (instead of stopping when I hit it, which is expected), and fell through him. I repeated that process about five times before I realized that it was an engine quirk. My geuss is that it's mmf2's default platform behavior. Not that much of a big deal (for this game) anyway, just a minor annoyance.
-Killing enemies just didn't feel satisfying. I prefer a bit more oomph when an enemy dies. Enemy death also felt a bit glitchy at times (The birds have an animation issue when they die.).
-Transitions between areas. Going up into the clouds and then back down again doesn't keep me in the same relative place.
What I love,
-The dialogue: I didn't get a couple, but most jokes were hilarious. I loved the shrooms, and Jables's flat responses.
-The music: It's very fitting, non obtrusive, and catchy as hell. I found myself humming it a while after I stopped playing the game.
-The sprites: Your style is awesome.
As a whole, It's a fun game that's worth playing till the end. I kept wanting to progress just to see what new characters and music I'd come across. Great job, and thanks, I had fun and enjoyed some laughs. Keep making games like this, and keep improving on the technical side! (You've got creativity covered
).