Saga, first introduced in Dominaria, is one of the newer Magic The Gathering mechanics. They're used to tell a story about the world rather than just having an effect on the game board, but they're also not really explained to new players very well. That's where we come in, detailing exactly how Saga cards work.
What are Sagas?
Sagas are a type of enchantment that once they enter the field, gain lore counters. You place your first lore counter on the card as it enters the battlefield, and then place another one during your draw step.
These cards have multiple different effects that trigger based on the number of lore counters on your card and then sacrifice themselves after they complete their story.
How do Sagas work?
Sagas don't work how you might think they work. Firstly, you need to pay the mana cost to activate them, the same as any other enchantment. Once they enter the field, though, they automatically activate as lore counters are added each turn. You do not have to pay the mana cost every turn to activate them.
It's also important to know that if you somehow find a way to remove a counter from a Saga, and then you add one, you'll actually trigger whatever effect links to that counter again. You won't automatically be moved onto the next stage of the counter until you have the necessary amount of lore counters.