Some good suggestions, thanks!
man i've heard stories about you and your site but never what exactly you did
Back in '11-'13 JDCGames started as a place to organise the collaboration hack I was running back then. It sort of evolved beyond that point and sustained its own community of ~30 active users. JDCGames Collab 1 did eventually get finished although unfortunately it's not the best
hack ever as it suffers from a high/unfair difficulty spike.
Overall, good job but I'd suggest adding this to the bounce blocks you used for the mushroom caps:
The bounce blocks are a little janky and do need to be tweaked. Fireballs also run right through the block as if it were invisible. Good shout about the sound effect and I'll edit that in.
I can't say much about Melancholy Mine because of it being just images, but the overuse of skull blocks does lowkey ruin the aesthetic. I'd suggest replacing them with spikes and spikes with wood beam backgrounds.
Yeah, I agree the skull blocks are lame. I did experiment with flipped Munchers and also spikes but they look worse. I made a small palette change incorporating red and blue shades of blocks to match the colours of the crystals in the level. I think this looks marginally better.
I've finished it now - except for some short playtesting and polishing. Here are some updated screenshots.
There are some creative ways I've used those two main platform sprites. It starts off simple in the 1st screenshot. The 2nd one shows Mario quickly moving up a section of platforms while avoiding straying too far right and hitting the skull blocks. The 3rd screenshot shows a section where you'll have to go left to access a bonus room & 1up. The final section of the level is a gauntlet where Mario has to traverse between several platforms while avoiding obstacles in his path. The secret exit to this level (not shown) requires Mario to use L/R to spawn/despawn platforms in a short puzzle.