Coincidentally, I came up with the idea to upgrade it on my own, without even having read this comment. The take-home lesson here is, of course, that I need to read comments more often.
And yes, there will probably be enemies at some point. Or at least, there will probably be walking obstacles that can be destroyed. (Not sure if there's a difference.)
You can do this by changing the level data. Just find where it says "cost_Coin_x5" and change that to whatever number you have in mind.
You can also replace "Coin," if you like. "cost_Jump_x2" would make them give up two of their jumps when they picked up the new power-up or item.
Hey man I don't know if you look at your comments, but I have some ideas for you, 1. Grappling hook, aim with the mouse, or part of the keyboard. 2. Rope swinging (It could be Chains, rope or just blocks xD.) 3. Guns and enemy's, all I need to say.
1. Good idea. It shouldn't be that hard to do, either.
2. Sounds a lot like #1. Perhaps after you use a grappling hook the rope can be left in place.
3. I'm thinking about whether this game should have combat. I'm leaning towards yes, but it wouldn't be gun-based combat, for the most part.
 "Power-up (prototype)"){kind=icon}
 "Mega4kMan"){kind=icon}
 "Sick Leave"){kind=icon}
 "Grand Theft Chicken"){kind=icon}
 "Cubes! (In Space)"){kind=icon}
 "Just Another Platformer 5"){kind=icon}
 "Platform Mania"){kind=icon}
 "Scary maze 2"){kind=icon}
 "Robot want game!"){kind=icon}
 "Exit Path"){kind=icon}
 "DuckLife2: World Champion"){kind=icon}
I've added background gradients for now, plus functionality for background images. Now I just need to _make_ said background images.