Nova the Squirrel by NovaSquirrel

Nova the Squirrel is a platformer game for the Nintendo Entertainment System, playable in an emulator (such as Mesen) or on a flashcart such as RetroUSB’s PowerPak. 
Explore 33 levels and fight 7 bosses across five different worlds in an attempt to save the world of Latte from the evil “Scheme Team”.

• Copy the abilities of your enemies. (10 in all!)
• Over 35 different types of enemies, plus variants.
• Interesting puzzle mechanics.
• Fancy soundtrack full of effects, by Vuurniac Squarewave.
• Modern design: no lives or time limits, tons of checkpoints.
• A collectible in every stage for those wanting a challenge.
• Bonus challenge levels after the main game.
• Bonus game: Double Action Blaster Guys.

This game is open source! You can find its source code at its  GitHub repository. While the tools are not very user-friendly yet, if you feel like getting into the code you can build new levels for the game with a drag-and-drop level editor, or modify the game as you please. Here is a second repository that’s intended to be a more generic version of the engine, meant to be a cleaner starting point for a new game.