The Pirate King has appeared as a Character in previous sets, but OP-13 marks his first playable Leader (OP13-003)
Rosheen Meanderer is another incentive to cast hydras with X in their mana cost
Kakamora Menacing Sailor Kakamora is hardly the first character to drop your opponents lore down when played, but that ability is still pretty cool regardless
Weve seen some good use of this style of card before, so I expect to see one or two of these make it in Constructed formats
Mana Geyser, Treasure makers, and so on can power out monstrous dragons, Eldrazi, an Ugin or two one of the best ways to use excessive ramp is to draw a ton of cards, either to convert that ramp into card advantage, or to ensure you have a bunch of ways to use your temporary mana
There's a charm captured in the pre-Modern frame, and some collectors love it