Mario Crossover: Kiss Your Day Goodbye
This may be the greatest flash game ever created. Instead of being stuck with Mario, you can play as Ryu (Ninja Gaiden), Link (Zelda), Bill R. (Contra), Simon (Castlevania), Mega Man, and Samus (Metroid). You keep all the different powers the characters normally have. Click the link below and say goodbye to productivity. Shouts to GruberSauce for the link!