How do you unlock this? I assume there is a hammer in the game, but I cannot find it. Thanks in advance.

It has no cards

I noticed that when I complete some levels, the circle on the map turns yellow, but for at least one it turns green. I guess green means "complete" and yellow means "something still remains", but what? I got the chest on Walkabout, but it's still yellow, for example....

Will have to check it out. Probably deserves more attention...

Avenger Bird support some generic controllers, but if you are having problems with not bad button configuration, you can manually change controller settings: Right click on a game and choose "Properties". Then choose "Set Launch Options" In the field enter "-show-screen-selector". After running the game you will see a launch window and in "Input" tab you can set your own gamepads and keys: Horizontal, Vertical - controls player movement, RHorizontal, RVertical - used for looking with camera. Fly - button...