Threnody Singer
Creature — Siren
Flash
Flying
When Threnody Singer enters the battlefield, target creature an opponent controls gets -X/-0 until end of turn, where X is your devotion to blue. (Each in the mana costs of permanents you control counts towards your devotion to blue.)
イラスト：
Theros Beyond Death#75アンコモン英語適正
裁定
The 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 blue changes.
Colorless and generic mana symbols (
, 
, , 
, 
, and so on) in mana costs of permanents you control don’t count toward your devotion to any color.
Mana symbols in the text boxes of permanents you control don’t count toward your devotion to any color.
Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).
If 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.
If 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.