Within a Deep Forest
From author's description: "Two attempts have been made to build a bomb, capable of freezing the entire world. The first was a failure, and resulted in a living blue ball. The second attempt was a success. Now the clock is ticking, and the world is in grave danger. That is, unless...
Within a Deep Forest is a freeware 2D platform game for Windows featuring challenging gameplay, beautiful music, an evil doctor, and a deep forest."
A walkthrough by Ghin was previously available on Nifflas' site at http://www.ni2.se/withinadeepforest/guides/ghin_walkthrough.txt, but that has since been taken offline. However, it was archived by the wayback machine and is still available here (Local Mirror 19th Jan '08).