Sometimes called Elder Dragon Highlander (EDH), Commander is a format where you have a legendary creature (your commander) at the head of a 100-card deck based around it. All the cards in the deck must have the same "color identity" as the commander and you can only play one copy of each card (except basic lands). The format is also multiplayer as opposed to 1 vs. 1 and you start with 40 life, making this format radically different from other Magic: the Gathering formats.