Vampire Nocturnus supports the mostly black cards contained in the deck, buffing vampires by +2/+1 and granting them flying as long as the top card of your library is black
Battles which, at least in their initial incarnation in March of the Machine, are all specified as the Siege type are an entirely new type of card, let alone double faced card
cEDH Subreddit has redditors that are competitors
(The tribal card type, now kindred, would be one of the ways we did this in the final set.) First, I asked myself, "What if we had spells that could turn into creatures?" Imagine a direct-damage spell that could become a Goblin
Staples are how you create consistency anyway: every deck runs a Sol Ring, a board wipe, some spot removal (and often a tutor or two to find them), so the average game plays smoothly even though no two decks are identical