Treasures are a specific type of token. When using Treasures, you tap one, sacrifice it, and add one mana of the color you choose to your mana pool. Treasures skip the stack, so there's no way to counter them.
Card rarity in Magic: the Gathering is more complicated than just Common, Uncommon, Rare, and Mythic Rare cards. Read on to learn the ins and outs of card rarity in Magic.
The Legend Rule makes it so you can only have one copy of a specific Legendary Creature on your board at a time, the rest are put in a limbo state in the graveyard.