Ice Cauldron — ruling 1

The Cauldron counts only mana spent on it. It doesn't see the value of X, so isn't affected by cost reductions. Thus, if you spent {C}{C}{R}{R} on X, you get {C}{C}{R}{R} later even if X was 6.

Ice Cauldron — ruling 2

Cards which are not actually in your hand can't be exiled by the Ice Cauldron.

Ice Cauldron — ruling 3

If multiple cards are exiled by the Cauldron, the mana can only be used for the card that was exiled by the Cauldron when the most recent charge counter was put there.

Ice Cauldron — ruling 4

The mana put in the Cauldron can only be used to cast the given spell, but you can add additional mana to a spell. This means you can pay part of the cost on one turn and the rest of it on the next turn.

Ice Cauldron — ruling 5

You do not have to use any mana from the Cauldron when casting the spell if you don't want to. You don't even have to tap the Cauldron and draw the mana, you can just cast the spell using mana from somewhere else.

Ice Cauldron — ruling 6

If multiple cards are exiled by the Cauldron, any one of them can be cast.

Ice Cauldron — ruling 7

If the ability to exile a card with the Cauldron is countered, you do not lose the card since it is exiled during resolution.

Ice Cauldron — ruling 8

It is possible to have more than one card exiled by the Cauldron. You can tap the Cauldron to remove the charge counter and whatever mana is on it but leave the card there. Later, you can tap it and put in mana and a charge counter to add another card.

Ice Cauldron : règles, fonctionnement et interactions (MTG)

Ice Cauldron 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

, : You may exile a nonland card from your hand. You may cast that card for as long as it remains exiled. Put a charge counter on this artifact and note the type and amount of mana spent to pay this activation cost. Activate only if there are no charge counters on this artifact. , Remove a charge counter from this artifact: Add this artifact's last noted type and amount of mana. Spend this mana only to cast the last card exiled with this artifact.

How it works : Ice Cauldron

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2004· Wizards of the Coast
The Cauldron counts only mana spent on it. It doesn't see the value of X, so isn't affected by cost reductions. Thus, if you spent on X, you get later even if X was 6.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
Cards which are not actually in your hand can't be exiled by the Ice Cauldron.
No other card is named in this ruling.
#3October 4, 2004· Wizards of the Coast
If multiple cards are exiled by the Cauldron, the mana can only be used for the card that was exiled by the Cauldron when the most recent charge counter was put there.
No other card is named in this ruling.
#4October 4, 2004· Wizards of the Coast
The mana put in the Cauldron can only be used to cast the given spell, but you can add additional mana to a spell. This means you can pay part of the cost on one turn and the rest of it on the next turn.
No other card is named in this ruling.
#5October 4, 2004· Wizards of the Coast
You do not have to use any mana from the Cauldron when casting the spell if you don't want to. You don't even have to tap the Cauldron and draw the mana, you can just cast the spell using mana from somewhere else.
No other card is named in this ruling.
#6October 4, 2004· Wizards of the Coast
If multiple cards are exiled by the Cauldron, any one of them can be cast.
No other card is named in this ruling.
#7October 4, 2004· Wizards of the Coast
If the ability to exile a card with the Cauldron is countered, you do not lose the card since it is exiled during resolution.
No other card is named in this ruling.
#8October 4, 2004· Wizards of the Coast
It is possible to have more than one card exiled by the Cauldron. You can tap the Cauldron to remove the charge counter and whatever mana is on it but leave the card there. Later, you can tap it and put in mana and a charge counter to add another card.
No other card is named in this ruling.
#9October 4, 2004· Wizards of the Coast
X can be zero. This places a zero mana counter on the Cauldron.
No other card is named in this ruling.
#10October 4, 2004· Wizards of the Coast
You can only cast the spell when you could legally cast it normally. So no casting a sorcery on your opponent's turn.
No other card is named in this ruling.
#11October 4, 2004· Wizards of the Coast
The mana can be used to pay for additional costs to cast the spell.
No other card is named in this ruling.
#12October 4, 2004· Wizards of the Coast
If the Cauldron leaves the battlefield, you can still cast any cards it exiled as though they were in your hand. You just no longer have access to the mana you charged the Cauldron with.
No other card is named in this ruling.
#13October 4, 2004· Wizards of the Coast
Tapping the Cauldron for the mana is a mana ability.
No other card is named in this ruling.
#14October 4, 2004· Wizards of the Coast
Produces mana of the last type used to put a counter on itself, not via any other charge counters.
No other card is named in this ruling.