Looks fun! BUT...if you're going to have really long levels like you said, you might not want the player to go ALL the way back to the beggining of the level. Maybe a checkpoint, or 10

and you might want to edit the sprite for Jack and get rid of the shadow underneath him. looks kinda funky when he jumps
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goodluck!
Working on a probably too ambitious project! Wild-west-adventure-RPG-shooter-thing.