Treasure Keeper
Artifact Creature — Construct
When this creature dies, reveal cards from the top of your library until you reveal a nonland card with mana value 3 or less. You may cast that card without paying its mana cost. Put all revealed cards not cast this way on the bottom of your library in a random order.
James Paick
Masters 25 (A25)
• #235Rulings
If a card in a player's library has {X} in its mana cost, X is considered to be 0.
(wotc • 2020-08-07)
If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
(wotc • 2020-08-07)
If you don't cast the nonland card with mana value 3 or less, it'll be put on the bottom of your library in a random order with the other cards.
(wotc • 2020-08-07)
If your library has no nonland cards in it with mana value 3 or less, you'll reveal all the cards in your library, then put them back in a random order.
(wotc • 2020-08-07)
If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
(wotc • 2020-08-07)
Rulings
If a card in a player's library has {X} in its mana cost, X is considered to be 0.
(wotc • 2020-08-07)
If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
(wotc • 2020-08-07)
If you don't cast the nonland card with mana value 3 or less, it'll be put on the bottom of your library in a random order with the other cards.
(wotc • 2020-08-07)
If your library has no nonland cards in it with mana value 3 or less, you'll reveal all the cards in your library, then put them back in a random order.
(wotc • 2020-08-07)
If you cast a spell "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, those must be paid to cast the spell.
(wotc • 2020-08-07)