Fathom

Adam Atomic created Canabalt. Adam Atomic created an obsession. Adam Atomic rules. Fathom is from him too, and while it's not as instantly obsessive, it's still pretty darn snazzy. You have on the surface a basic platformer but when you meet the first level boss things change.

The next level is underwater and you use your weapon (steady) to propel yourself around exploring. there are fish knocking about who will 'follow' you, and the dark comes along when you go deep enough... the endless dark.

Use the arrow keys to move around. In the first level press 'z' to jump and 'x' to fire, then in the second use 'z' to turn your torch on and 'x' to propel yourself.

Those fish could help you, you know.