This is kind of a dumb argument, but being official just means that the program will have the most support, the biggest team modifying it, and itll ultimately run the best
Songs tend to have especially powerful effects and, unlike normal actions, you can play them for free by having one of your characters exert to sing the Song instead
Then each player takes two cards from the other players pack and trades back
For the Mike side of the equation, here are the sort of creatures Im going to want to have around to bring back with his ability: There are all sorts of creatures with awesome enters the battlefield abilities to bring back with Mike, but the ones I highlighted above help keep your hand full, which is what we want with Eleven
Always check if a card actually exists in the format or version youre buying
They each come with their own advantages and disadvantages