The Cauldron of Eternity — ruling 1

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.

The Cauldron of Eternity — ruling 2

The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.

The Cauldron of Eternity — ruling 3

Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.

The Cauldron of Eternity : règles, fonctionnement et interactions (MTG)

The Cauldron of Eternity is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

This spell costs less to cast for each creature card in your graveyard. Whenever a creature you control dies, put it on the bottom of its owner's library. , , Pay 2 life: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.

Complete guide

The Cauldron of Eternity is a legendary artifact that offers powerful recursion for decks that fill their graveyards with creatures. While its initial mana cost seems daunting, it rewards graveyard-centric strategies by becoming significantly cheaper for every body waiting in the pits. However, this power comes with a unique drawback: once the Cauldron is active, your fallen soldiers will bypass the graveyard and head straight back to the library.

Understanding the Cost Reduction

The Cauldron of Eternity features a static ability that reduces its casting cost by {2} for every creature card currently in your graveyard. It is important to note that this only reduces the generic mana portion of the cost. Even if you have five or more creatures in your graveyard, you must still pay the {B}{B} required to cast it. Once you begin the process of casting the spell, opponents cannot remove cards from your graveyard to increase the cost, as the total cost is locked in before priority is returned to other players.

The Death Replacement Trigger

The second ability is a triggered ability that triggers whenever a creature you control dies. Instead of staying in the graveyard where you can reanimate it, the creature is moved to the bottom of its owner's library. Because this is a triggered ability and not a replacement effect (like 'instead'), the creature does briefly hit the graveyard before being tucked away. This is crucial for other cards that care about 'whenever a creature dies' triggers.

Reanimating the Fallen

The final ability allows you to spend {2}{B}, tap the Cauldron, and pay 2 life to return a target creature card from your graveyard to the battlefield. This can only be done as a sorcery, meaning during your main phase while the stack is empty. Because the Cauldron's second ability puts dying creatures on the bottom of your library, you will mostly be targeting creatures that were in your graveyard before the Cauldron entered the battlefield or cards that were milled directly into the graveyard.

Interaction examples

Cost Reduction Efficiency

Excalibur, Sword of Eden

If you have four creature cards in your graveyard, The Cauldron of Eternity costs {2}{B}{B} to cast. If you then play Excalibur, Sword of Eden, the Cauldron contributes to the cost reduction of Excalibur because the Cauldron is a Legendary Artifact (a historic permanent). This pair rewards high-mana-value permanents that can be cheated into play for low costs.

Interaction with Replacement Effects

Blightsteel Colossus

If you control both cards and Blightsteel Colossus would be put into the graveyard, its own replacement effect occurs: it is revealed and shuffled into the library instead of ever hitting the graveyard. Because the Colossus never technically 'dies' (it never hits the graveyard), The Cauldron of Eternity's second ability will not trigger, and the Colossus will be shuffled rather than put on the bottom.

Using the Activation

Suppose you have a creature card in your graveyard that was milled there by an opponent. On your turn, you pay {2}{B}, tap the Cauldron, and pay 2 life. You target that creature card. As the ability resolves, the creature enters the battlefield. If that creature later dies while you still control the Cauldron, the Cauldron's triggered ability will fire, putting that creature on the bottom of your library.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : The Cauldron of Eternity

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2019· Wizards of the Coast
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
No other card is named in this ruling.
#2October 4, 2019· Wizards of the Coast
The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.
No other card is named in this ruling.
#3October 4, 2019· Wizards of the Coast
Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.
No other card is named in this ruling.