Masked HERO Acid

 This card bears a strong resemblance to Kamen Rider Ibuki from the Kamen Rider Hibiki series,  from Kamen Rider Decade and Kamen Rider Ixa's Rising Ixa form from Kamen Rider Kiva.

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Notably these are all second riders with blue being the dominate color of their color scheme.

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This monster's effect is opposite to the effect of the Elemental HERO Absolute Zero:

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This card gets its 1st effect when it is Special Summoned whereas Elemental HERO Absolute Zero gets its effect when it leaves the field.

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This card destroys Spell and Trap Cards whereas Elemental HERO Absolute Zero destroys monsters.

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This card lowers opponent's monsters ATK whereas Elemental HERO Absolute Zero gains ATK.

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This card's effect name is Acid Rain, while its attack name is Acid Bullets.

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OCG Rulings

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The ATK reduction lasts as long as each affected monster remains face-up on the field.: Effect Monster > Masked HERO Acid

If the effect of multiple copies of Masked HERO Acid are activated, the ATK reduction is cumulative.

If the effect of Masked HERO Acid cannot destroy the Spell/Trap cards the opponent controls, it does not reduce the ATK of the opponent's monsters by 300. Also, if the effect of Masked HERO Acid destroys at least 1 Spell/Trap card the opponent controls, it will reduce the ATK of the opponent's monsters by 300. Furthermore, if at the time of the resolution of the effect of Masked HERO Acid the opponent doesn't control any monsters, all Spell/Trap cards the opponent controls are still destroyed.: If the effect of Masked HERO Acid cannot destroy the Spell/Trap cards the opponent controls, does it still reduce the ATK of the opponent's monsters by 300?
Also, if at the time of the successful Summon of Masked HERO Acid the opponent does not control any monster, are all the Spell/Trap cards controlled by the opponent still destroyed?