All-Seeing Arbiter
Creature — Avatar
Flying
Whenever this creature enters or attacks, draw two cards, then discard a card.
Whenever you discard a card, target creature an opponent controls gets -X/-0 until your next turn, where X is the number of different mana values among cards in your graveyard.
Robin Olausson
Rulings
The mana value of a double-faced card in your graveyard is always the mana value of the front face.
(wotc • 2022-04-29)
The mana value of a land card is 0.
(wotc • 2022-04-29)
The mana value of a split card in the graveyard is the total mana value of both halves of that card. It does not have two mana values.
(wotc • 2022-04-29)
X is 0 when determining the mana value of a card in your graveyard.
(wotc • 2022-04-29)
Rulings
The mana value of a double-faced card in your graveyard is always the mana value of the front face.
(wotc • 2022-04-29)
The mana value of a land card is 0.
(wotc • 2022-04-29)
The mana value of a split card in the graveyard is the total mana value of both halves of that card. It does not have two mana values.
(wotc • 2022-04-29)
X is 0 when determining the mana value of a card in your graveyard.
(wotc • 2022-04-29)