ハイドラの繁殖主
クリーチャー — ハイドラ
：怪物化Ｘを行う。（このクリーチャーが怪物的でないなら、これの上に＋１/＋１カウンターＸ個を置く。これは怪物的になる。）
ハイドラの繁殖主が怪物的になったとき、緑のＸ/Ｘのハイドラ・クリーチャー・トークンＸ体を生成する。
イラスト：
Commander 2021#194レア日本語適正
裁定
The value of each X in Hydra Broodmaster’s last ability is equal to the value chosen for X when its monstrosity ability was activated.
Once a creature becomes monstrous, it can’t become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.
Monstrous isn’t an ability that a creature has. It’s just something true about that creature. If the creature stops being a creature or loses its abilities, it will continue to be monstrous.
An ability that triggers when a creature becomes monstrous won’t trigger if that creature isn’t on the battlefield when its monstrosity ability resolves.