To unlock all medals, you have to complete all game achievements. I will list them and say when you'll got a medal too.
THE END
Finish all levels, and you'll get the medal too
A LITTLE BIRDIE TOLD ME
In the menu page, click on Spread the game, then on the Tweeter button (the one with the blue bird, just in case...). Medal too.
BLOODBATH
Kill 150 little characters on the loading page. If you need to come back to this page, do not close and restard, you'll just need to hit F5. Medal too.
UNLOCKNESS
Go in the achievement page after unlocked all other achievements. Medal too.
THERE IS NO REPLAY
Go to level select - ATHEISM. Kill the character, then click the replay button. It's over the red writing in the right corner.
PIECE OF CAKE
Go to level select - EPICROLL. When the numa numa singer will be on screen, click on the white cook hat on the left. It's the easier way, or you can just wait after Obama song (you'll need to see, don't ask) and click quickly the cook before the numa numa singer appears.
WHERE THE HELL IS MONA?
This was really hard to discover. Go to level select - ART. Click on that mona. Imagine me clicking on hundreds of mona before finding the right one.
I do apologise if my english is not as good as it should be, but it's Berlusconi's fault because in Italy we do not learn foreign languages at public school.
Roland7749
THANK YOU!