Thestalos the Firestorm Monarch

 This monster has a Vassal counterpart: Berlineth the Firestorm Vassal.

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The names of both this card and Berlineth the Firestorm Vassal are derived from the names of cars produced by Ferrari. Specifically, this card's name is derived from the Ferrari Testarossa, a series of sports cars that was preceded by the Ferrari Berlinetta Boxer.

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This monster has an upgraded form: Thestalos the Mega Monarch.

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This monster appears in the artworks of March of the Monarchs, Domain of the True Monarchs and Tribute Carnival.

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TCG Rulings

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Lifeforce Harmonizer: 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.

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OCG Rulings

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The effect of "Lifeforce Harmonizer" cannot be activated against an effect which may or may not inflict damage, like "Thestalos the Firestorm Monarch

Previously Official Rulings

If you Tribute Summon "Thestalos the Firestorm Monarch" successfully, and your opponent discards a monster like "Outstanding Dog Marron" or "Regenerating Mummy", you still inflict damage because the monster was discarded to the Graveyard (even though it doesn't remain there).

This card's effect always activates when Tribute Summoned, even if your opponent has no cards in their hand.: Are Mandatory Trigger Effects forced to Activate?

Gemini Imps: If your opponent Tribute Summons “Thestalos the Firestorm Monarch”, you can chain with the effect of “Gemini Imps”. The effect of “Thestalos the Firestorm Monarch” would be negated and it would be destroyed, and then you would draw a card.

Monarch's" effects activate at the time they are successfully Tribute Summoned. Their effects are Spell Speed 1. If the opponent wants to activate a card like "Bottomless Trap Hole", it will be placed onto the Chain with the "Monarch's" effect. But "Monarchs" don't need to remain on the field to resolve their effects, so destroying them with "Bottomless Trap Hole" will not negate their effect.: Bottomless Trap Hole Vs. Monarchs

When you Tribute a monster with a mandatory Trigger Effect that activates as a result of the monster being Tributed, the Tributed monster's effect is placed first on the Chain. So, if you Tribute your opponent's "Sangan" (due to "Soul Exchange") for the Tribute Summon of "Thestalos the Firestorm Monarch", "Sangan" is placed first onto the Chain because its Trigger Effect activated when it was Tributed, followed by "Thestalos the Firestorm Monarch".: Sangan vs. Soul Exchange vs. Thestalos: soul exchange; gravekeeper's servant w/ Macro Cosmos/Dimensional Fissure]

If "Banisher of the Light" is face-up on the field, no damage is inflicted because the card is not discarded to the Graveyard.The latest print of this card has Problem-Solving Card Text, which does not state that the discarded card has to be sent to the Graveyard in order for damage to be inflicted, making this ruling invalid.