This is definitely going to be my favorite platformer of the jam. Jump is well designed and you had a neat core mechanic. I thought it was going to be exactly like Cockatune at first but realized on level 3 that you can still jump regularly haha. The fully explodable sections and keys that you have to explode to open doors are really good mechanics that build on the core one. Other small graphical details I really appreciated too like the count down timer becoming a slightly brighter red as it counted down and the background wave and the foreground wave at different shades of green and speeds.
Also love the fact that you had bonus hard levels, they were a good challenge, the timing on the last one was especially tight. Do you have any favorite platformers that inspire you?
One minor suggestion is that the spikes should be colored something different from the walls since I wasn't sure if they were spikes at first and even afterwards it was a bit hard to immediately parse a level because of their color. Probably something close to pure white would be good if pure white is too bright for the game's palette.