Sheoldred // The True Scriptures

(As this Saga enters and after your draw step, add a lore counter.)
I — For each opponent, destroy up to one target creature or planeswalker that player controls.
II — Each opponent discards three cards, then mills three cards.
III — Put all creature cards from all graveyards onto the battlefield under your control. Exile The True Scriptures, then return it to the battlefield (front face up).

Menace
When Sheoldred enters, each opponent sacrifices a nontoken creature or planeswalker of their choice.
{4}{B}: Exile Sheoldred, then return it to the battlefield transformed under its owner's control. Activate only as a sorcery and only if an opponent has eight or more cards in their graveyard.

March of the Machine

Menace
When Sheoldred enters the battlefield, each opponent sacrifices a nontoken creature or planeswalker.
{4}{B}: Exile Sheoldred, then return it to the battlefield transformed under its owner's control. Activate only as a sorcery and only if an opponent has eight or more cards in their graveyard.

March of the Machine Promos

Once you’ve activated Sheoldred’s last ability, it doesn’t matter what happens to the number of cards in opponents’ graveyards. The ability will resolve even if no opponent has eight or more cards in their graveyard by that time.

To resolve Sheoldred’s enters-the-battlefield ability in a multiplayer game, the next opponent in turn order (or, if it’s an opponent’s turn, the opponent whose turn it is) chooses a creature they control to sacrifice. Then each other opponent in turn order does the same. Then those creatures are sacrificed at the same time.

To resolve chapter II of The True Scriptures in a multiplayer game, the next opponent in turn order (or, if it’s an opponent’s turn, the opponent whose turn it is) chooses three cards in hand. Any opponent who has fewer than three cards in hand chooses all cards they have in hand. They set the chosen cards aside without revealing them. Then each other opponent in turn order does the same. Next, all chosen cards are revealed and discarded at the same time. Then, each opponent mills three cards.

You can activate Sheoldred’s last ability if any opponent has eight or more cards in their graveyard, not necessarily all of them.