Duskmourn: House of Horror is the first non-Innistrad-based set to use delirium as a full mechanic, and it adds an interesting spin
Battlefield: This is the main play area of the game, where all your creatures, artifacts, lands, and other cards go after you cast them, and where war will be waged against whatever forces your opponent can muster
If you pass an Abzan Charm, it shouldn't come as a great surprise if you later find out that a player you were passing to drafted Abzan
Yes, Vampire Commander decks can be competitive, especially those led by Edgar Markov or Anje Falkenrath
Because of its large amount of low-Willpower characters, it's also fairly susceptible to removal actions like Grab Your Sword