[egypturnash]

Practice and exposure. Having fun with your friends.

If you look at the spreadsheet at https://docs.google.com/spreadsheets/d/1Tn3PNewzF4t2nT9etXeq... then you'll notice that there's about four hundred people involved, most of whom did a mere two pages. That's really not a ton of work for any one artist.

If you go to a comics convention you will find a ton of stuff along these lines, at a smaller scale - here's two or three things you like, put together in a funny way, maybe you'll buy that, maybe that'll draw you in to a person's table to look at their original work and become a new fan of theirs. Batman but it's Adventure Time? A DeLorean driving out of the TARDIS? Portal but it's the Muppets? Whatever.