I've never seen either Family Guy or American Dad! (or most any other show in the eight years since I cancelled my television service), but even I marvel at the sheer genius and execution of this crossover promotion:
Check out this 1- or 2-player, Street Fighter-style, Flash-based fighting game. Wild!
(As a side note: can anyone identify what remix version of Carl Douglas' song is playing in the background of this game's title screen?)