How about a 100% or all easter eggs run where you have to go and find all the easter eggs in the game ether as it's own, or as part of beating the game 100%. This should be done on Steam with an account with no achevments for Ather gotten for it that has to do with achevments, and you can see if You've 100%'ed a game on the Basement collection menu if there is a black star above the game.

This can be done once only, so it's not the best deal