Cheapest priced copy (Streets of New Capenna Promos): $0.99 at Card Kingdom, near mint, their price list as of .
All-Seeing Arbiter 
Creature — Avatar · 5/4 · Mythic · Streets of New Capenna Promos · #34p
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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.99 to $7.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Game Day Promos | 3 | Mythic | — | $7.49 |
| Streets of New Capenna Promos | 34p | Mythic | $0.99 | $1.99 |
| Streets of New Capenna Promos | 34s | Mythic | — | $0.99 |
| Streets of New Capenna | 34 | Mythic | $0.99 | $0.99 |
| Streets of New Capenna | 286 | Mythic | $0.99 | $2.49 |
4 rulings from Wizards of the Coast
- 29 April 2022The mana value of a double-faced card in your graveyard is always the mana value of the front face.
- 29 April 2022The mana value of a land card is 0.
- 29 April 2022The 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.
- 29 April 2022X is 0 when determining the mana value of a card in your graveyard.