Nice game. A bit fast-paced, but that's okay if that's how you designed it. The story in the intro page (along with the puns) was nice. It might be nice to have a picture of Jumpkin bringing the Pumpking back home for the win screen to tie in with the intro.
When I get to the end of a level, for a moment, it feels like I lost, but then I find myself in the next level, so I figure that I'm okay. It might be nice to save the level of the player after he dies so that he won't have to go through previous levels again. I liked the enemy explosion effect.
Displaying the lose screen immediately after falling into a pit felt a little bit sudden. Showing the player fall for a second might help the player understand why he lost a life.
I couldn't figure out what the pick-ups did. Maybe some game juice would be good when you pick one up (e.g. cool power-up animation). Maybe one could unlock a fire-breathing ability (via Jack'o lantern candle) to burn baddies with.
I found that if you hold the forward button down and press the jump key a lot, you get to cruise through each level like a breeze (otherwise, it's very hard to get past bad guys). However, there is a bug where, while doing this, you can fly off the top of the screen. After this, the game crashes and gives the following error:
Maybe you could clamp the position of the player to keep him within the boundaries of the screen to fix the bug.
Thanks for sharing the game!