MTG Treachery

The Great Martyr’s replacement effect redirects all damage to you and any results following that damage, like commander damage and poison counters from infect source.
If you don’t have enough cards to discard or permanents to sacrifice, you discard or sacrifice as much as you can, even if it’s nothing.
This ability affects sacrifices, but not any other ways permanents can leave the battlefield. It won’t stop a creature controlled by a Leader from being put into the graveyard due to lethal damage or having 0 toughness, and it won’t stop a permanent from being put into the graveyard due to the "legend rule." None of these are sacrifices; they’re the result of game rules.
If an effect your opponent controls reduces the maximum hand size of a Leader player, The Great Martyr’s replacement effect won’t apply and that Leader player still discards cards when the game rules cause them to discard during their cleanup step.
An effect that prevents you from losing life will apply and any damage redirected to you by The Great Martyr’s replacement effect will do nothing.

An effect that prevents you from discarding cards or sacrificing permanents (as Tamiyo, Collector of Tales does) will apply and any discard or sacrifice effect redirected to you will do nothing.
An effect that prevents a Leader player from losing life, discarding cards or sacrificing permanents may be applied before or after The Great Martyr’s replacement effect, as they choose.
If an effect from a source an opponent controls states that something happens unless a Leader player pays life, discards a card or sacrifices a permanent (as Mogis, God of Slaughter does), or if an effect from a source an opponent controls instructs a Leader player to pay life, discard a card or sacrifice a permanent unless they perform an action (as Killing Wave does), and they choose to perform the action, instead you lose that much life, discard that many cards or sacrifice that many permanents.
If a Leader player spends life, discards a card or sacrifices a permanent to pay a cost of an ability an opponent controls (such as Excavation), The Great Martyr’s replacement effect does not apply and that Leader player still pays the cost themselves.