Todeskuss

Immer wenn eine Kreatur, die ein Gegner kontrolliert, einen deiner Gegner angreift, verdopple ihre Stärke bis zum Ende des Zuges.
{X}{X}{R}: Monstrum X.
Wenn der Todeskuss monströs wird, stachle bis zu X Kreaturen deiner Wahl an, die deine Gegner kontrollieren.

Baiser de la mort

À chaque fois qu'une créature qu'un adversaire contrôle attaque un de vos adversaires, doublez sa force jusqu'à la fin du tour.
{X}{X}{R} : Monstruosité X.
Quand le Baiser de la mort devient monstrueux, incitez jusqu'à X créatures ciblées que vos adversaires contrôlent.

デス・キス

対戦相手がコントロールしているクリーチャー１体があなたの対戦相手１人を攻撃するたび、ターン終了時まで、それのパワーを２倍にする。
{X}{X}{R}：怪物化Ｘを行う。
デス・キスが怪物的になったとき、対戦相手がコントロールしているクリーチャー最大Ｘ体を対象とする。それらを使嗾する。

Death Kiss

Whenever a creature an opponent controls attacks one of your opponents, double its power until end of turn.
{X}{X}{R}: Monstrosity X. (If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.)
When Death Kiss becomes monstrous, goad up to X target creatures your opponents control.

Commander Legends: Battle for Baldur's Gate

Whenever a creature an opponent controls attacks one of your opponents, double its power until end of turn.
{X}{X}{R}: Monstrosity X.
When Death Kiss becomes monstrous, goad up to X target creatures your opponents control.

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.

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.

Once a creature becomes monstrous, it can't become monstrous again. If the creature is already monstrous when the monstrosity ability resolves, nothing happens.

To double a creature's power, it gets +X/+0, where X is its power as that ability resolves.