The exceptions to that rule are the Swords, like Sword of Fire and Ice or Sword of Feast and Famine
Yes, Sanguine Bond is a key card in 8 combo(s) in our combo database, linked from the Combos section of this page
Some cards in the set grant additional bonuses or abilities when a player reaches max speed, creating a sense of momentum and progression throughout the game
Kithkin in green-white, Merfolk in white-blue, Goblins in black-red, Elementals in blue-red, and Elves in black-green
Expansion It's any new set that brings new cards to the game, cards that didn't exist before, just to expand the range of card options when creating new decks