Cheapest priced copy (Mystery Booster 2): $23.99 at Card Kingdom, near mint, their price list as of .
Thassa's Oracle 
Creature — Merfolk Wizard · 1/3 · Rare · Theros Beyond Death Promos · #73p
When this creature enters, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $23.99 to $229.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mystery Booster 2 | 175 | Rare | $23.99 | $129.99 |
| Theros Beyond Death Promos | 73p | Rare | $29.99 | $34.99 |
| Theros Beyond Death Promos | 73s | Rare | — | $44.99 |
| Secret Lair Drop | 1280 | Rare | $139.99 | $229.99Out of stock |
| Theros Beyond Death | 73 | Rare | $24.99 | $34.99 |
| Theros Beyond Death | 308 | Rare | $37.99 | $79.99 |
6 rulings from Wizards of the Coast
- 24 January 2020Colorless and generic mana symbols ({C}, {0}, {1}, {2}, {X}, and so on) in mana costs of permanents you control don't count toward your devotion to any color.
- 24 January 2020If you put an Aura on an opponent's permanent, you still control the Aura, and mana symbols in its mana cost count towards your devotion.
- 24 January 2020If an activated ability or triggered ability has an effect that depends on your devotion to a color, you count the number of mana symbols of that color among the mana costs of permanents you control as the ability resolves. The permanent with that ability will be counted if it's still on the battlefield at that time.
- 24 January 2020If your devotion to blue is zero at the time the triggered ability of Thassa's Oracle resolves, you don't look at or move any cards in your library. If you have no cards in your library, you win the game.
- 24 January 2020Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
- 24 January 2020Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.