Hmm, the idea of the April Fool's day nasty surprise looks good. Reminds me of ADOM, where depending on which day you create a character, certain things can happen to you.
Maybe there should also be a "Creator's Day" feature where, if you start the game on Kornel's Birthday, you get a bonus.
Of course, starting the game on other days, like, for example, a Friday the 13th, or a day with a day number that ends in 6 (Catch the reference!), you get penalties, like being weaker, needing more XP to get a new trait, demons being stronger or respawning even while not on Nightmare Difficulty, etc.