Nova the Squirrel

Nova the Squirrel is an open source NES platformer game that features Kirby-style ability copying as well as puzzle platforming. It features 33 levels (plus several bonus levels at the end), seven bosses, and a collectible in every level the player can try to get for 100% completion. It has a modern design, featuring no time limits or lives, as well as an abundance of checkpoints and in-game help.