Cheapest priced copy (Theros Beyond Death): $0.35 at Card Kingdom, near mint, their price list as of .
Klothys's Design 
Sorcery · Uncommon · Theros Beyond Death · #176
Creatures you control get +X/+X until end of turn, where X is your devotion to green. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Theros Beyond Death | 176 | Uncommon | $0.35 | $0.49 |
7 rulings from Wizards of the Coast
- 24 January 2020Klothys’s Design affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +X/+X.
- 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 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 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 2020The value of X is determined only as Klothys’s Design resolves. Once that happens, the value of X won’t change later in the turn even if your devotion to green changes.