Would I be able to play this in response to an opponent casting a creature with an ability that triggers when it enters the battlefield, and keep the ability from triggering, since it no longer has the ability, or would the ability trigger before Turn to Frog would take effect?
Would I be able to play this in response to an opponent casting a creature with an ability that triggers when it enters the battlefield, and keep the ability from triggering, since it no longer has the ability, or would the ability trigger before Turn to Frog would take effect?
ETB the abilities trigger immediately when something enters the battlefield--this is long before you have priority to cast anything. So, the ability will be on the stack once you cast Turn to Frog.
You cannot target a creature spell with Turn to Frog , only a creature permanent. Which means, you can target the creature only after it has already entered the battlefield and therefore the ETB ability has already triggered. Tempering with the source of an ability in any way (removing it from the source, destroying the source, etc.) will not stop the ability, which exists independently on the stack.
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