Martyrdom is a keyword from the Final Fantasy set that lets you redirect damage to a creature with martyrdom. It reads: ": The next time a source of your choice would deal damage this turn, that damage is dealt to this creature instead." You activate this ability, choose a source, and the next damage that source would deal gets rerouted onto your martyrdom creature—protecting your other permanents, your planeswalkers, or your own face.
The key nuance people miss: you choose the source, not a specific instance ahead of time—it catches the next damage from that source, whether combat, a burn spell, or an ability. It doesn't prevent the damage; it just changes the recipient, so deathtouch, lifelink, and triggers still apply based on the new target.
In Commander, it shines defensively—soaking a big attacker, eating a removal-style burn spell, or absorbing damage to keep a key permanent alive. Just remember it taps the creature, so timing matters.