Cheapest priced copy (Theros Beyond Death): $0.35 at Card Kingdom, near mint, their price list as of .
Blight-Breath Catoblepas 
Creature — Beast · 3/2 · Common · Theros Beyond Death · #86
When this creature enters, target creature an opponent controls gets -X/-X until end of turn, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Theros Beyond Death | 86 | Common | $0.35 | $0.49 |
6 rulings from Wizards of the Coast
- 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.
- 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 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 2020The value of X is determined only as the triggered ability resolves. Once that happens, the value of X won’t change later in the turn even if your devotion to black changes.
- 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.