Kid Niki: Radical Ninja (aka The Wonderful Yanchamaru) was originally released in 1986 as an arcade game, then ported to the Nintendo Entertainment System (NES), Apple II, and the Commodore 64.
The game is about Kid Niki saving his lady love from the clutches of the evil Stone Wizard, in order to do that he has to battle his way into 7 rounds/stages, each one ends with a boss battle.
These Kid Niki papercrafts include Round 1 Boss "Death Breath", Round 2 Boss "Spike", and Round 4 Boss "Green Grub". I'm pretty sure the designer is going to complete this series, so stay tuned for that. Follow the link below and scroll to the middle of the page to get the goods. Thanks Bryan!