Cheapest priced copy (Born of the Gods): $0.35 at Card Kingdom, near mint, their price list as of .
Thassa's Rebuff 
Instant · Uncommon · Born of the Gods · #54
Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Born of the Gods | 54 | Uncommon | $0.35 | $0.79 |
4 rulings from Wizards of the Coast
- 15 September 2013Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
- 15 September 2013Numeric mana symbols ({0}, {1}, and so on) in mana costs of permanents you control don't count toward your devotion to any color.
- 15 September 2013Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.
- 15 September 2013If 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.