Ikachan

Ikachan (a.k.a. いかちゃん, "Little Squid") is a mini-game created by Daisuke Amaya before Cave Story. There are a few references in Cave Story towards the game, but the biggest one would be the cameo of a group of squid swimming by after defeating Ironhead without getting hit. If you manage to do this, you will get the item Alien Medal that has a picture of an Ikachan on it. This game was ported to the 3DS eShop.