This key is specifically for Awesomenauts Honeydew Skolldir Skin (based on the yogscast member who voiced character). It should also unlock the hero, as far as I can tell, so I put it under that tag. It used to be available for free only through newsletter, website and buying bundle, so now it's probably the only way to unlock it?

The game itself is sadly dead, so enter only for collecting/preservation purposes.

From Yogscast Jingle Jam 2015