I've digitally doctored one of my mezuzot so that there is now a mistake in every single one of the 22 lines. (This doesn't include the 4 letter name of God (Tetragrammaton) which I have doctored for other reasons)).
This is not an easy task, made even harder by the nature of an internet resolution jpeg. However, if you would like to have a go at finding all 22 mistakes or as many as you can, please do and contact me and I'll send you the list of errors. No prizes (at the moment) except the satisfaction of a job well done and maybe a mention on the site.
You may want to print it off and compare it with the correct version on the mezuzah page and perhaps after playing the game check your own homes mezuzot - you may be unpleasantly surprised!