(1) When your opponent activates a card's effect that inflicts damage, you can discard this card to negate its activation and destroy it.
The (1) Quick Effect can be activated during either player’s turn.
This effect can only respond to the activation of a card that is confirmed to inflict damage at resolution.
This effect can be activated if Caius the Shadow Monarch targets a face-up DARK monster.
This effect cannot respond to a card / effect that does not / might not inflict damage at resolution.
It cannot be used against the activation of "Wave-Motion Cannon" or the activation of the effect of "Wave-Motion Cannon" [REF].
It cannot be used against "Thestalos the Firestorm Monarch" since you don’t know if damage will be inflicted.
This is a Multi-Trigger Effect that can be activated during either player's turn.
This effect can only be chained to the activation of a card that is confirmed to inflict damage at resolution. It cannot be used against the activation of "Wave-Motion Cannon" or the activation of the effect of "Wave-Motion Cannon". It cannot be used against "Thestalos the Firestorm Monarch" since you don't know if damage will be inflicted.
If you control "Des Wombat" and it is preventing you from taking damage, you cannot activate "Lifeforce Harmonizer".
You can use "Lifeforce Harmonizer" on your opponent's card that inflicts damage to themselves, such as "Zombie Mammoth" if there is a situation where it will inflict damage to the opponent.