There's really no set way to go about it. This year though we (me and the D3 guys) wanted to make sure we had plenty of time to put out something that was media-intensive, movies, art, screenshots, etc. That all takes a lot of planning and time to execute when you're working between a few departments. All I knew is I wanted it to be as cool as the Tauren-marine page was last year, if not cooler.
So we started very early, like back in February. It wasn't really very formal to start, I was just kicking ideas around with an old buddy of mine some of you may remember from the old Battle.net days, NathanL, who is now a producer on Diablo III. The idea of a class reveal was obvious. It came down to making sure it was media intensive, with a bare minimum of impact on the team's current work flow. We couldn't have artists and animators pulled off the game to make unique models and textures for a one-off joke. So he threw out the idea of using Cain, who already had a near-full animation set, and making it some sort of weak class. The ideas just sort of flowed from there. What if a Cain-like character was a class? An old guy that liked to research and identify items, etc.
Originally we called it the Lore Master, then later I threw out Archivist. We had a few official meetings with production schedules and boring stuff and laid out all the ideas we wanted to hit with the media on the site. It all sort of went from there. Julian threw together the effects for Lorenado in, I swear, like 15 minutes. It was amazing. The DVD production guys shot all the video, hitting all the major points for what we wanted in each one. Mike Nicholson did the screenshots. Michael Chu wrote the lore. Phroilan Gardner did the concept piece. Everything goes through approval processes and translations. The web team puts everything together and runs a soft terrycloth towel over it, makes it all sparkly and nice looking. Finally, it's released, and we all breath a sigh of relief.
If it only takes 15 minutes to make a spell that cool that's only for a joke, I'm excited to see the real spells that'll be in the game