Force everyone to change theme and change the name, for we are now DigiCommunity and are all fans of Digimon!!!! Maybe a slogan: "Pokémon is so 1995". If possible, every Poké- prefix is replaced with Digi- (possibly requires some amazing PHP wizardry :) )
Other than that we could give everyone Admin banners (but not actually make them an admin :P ) just for lolz. Or change the Supporter tiers from 5 to say 9,871. We could also put out fake announcements for a Ruby/Sapphire remake, or Generation VI that uses mind control and virtual reality with the new Nintendo 4DS. Or maybe Ash finally dies in the next anime episode?
Something really whacky that peeps will remember. :D