Moat – MTGO Holiday Cube. You can play Moat on Magic Online right now through January 2 by participating in the Holiday Cube (more details). And you can get a wallpaper of the great new art in today's Arcana!
Wrecking Ball – Dissension common. The name "Wrecking Ball" is actually a pun. Because instead of being one of those giant metal balls that knocks down buildings, it's the kind of "ball" you have in a ballroom. But because it's Rakdos, the ballroom ends up getting knocked down anyway.
Avatar of Discord – Dissension rare. Note that Avatar of Discord requires that its caster actually have two cards to discard. If it said "When Avatar of Discord enters the battlefield, discard two cards," then you could get away with casting it as the last card in your hand. But you can't!
Rakdos, Lord of Riots – Return to Ravnica mythic rare. The Rakdos Cult is made up of Rings, which are informal groups of people who pay tribute to Rakdos. But the only real organization is that Rakdos is the undisputed leader.
Phantom General – Return to Ravnica uncommon. From a flavor standpoint, there's no difference between a creature represented by a token and a creature represented by a card. But for the purposes of Phantom General, ghosts mean tokens. Just for this one card, though!
Skyline Predator – Return to Ravnica uncommon. You can tell the difference between a drake and a dragon in Magic art by counting the legs. Dragons have four legs (and wings), while drakes are missing the front pair. Of course, if it's a creature card, you also have the option of looking at the type line.
Chromatic Lantern – Return to Ravnica rare. The power of the Chromatic Lantern is shown in its art: it appears to be casting off multiple colors of light at once. In fact, what it's actually casting off is mana! And also regular light, because you never know when you'll want a good lantern.
Avenging Arrow – Return to Ravnica common. Not all cards in Return to Ravnica belong clearly to one guild or another. Just because thisAvenging Arrow came from a Selesnya archer doesn't mean there couldn't be others that were from the Azorius. They also like punishing wrongdoers, after all!