Cavern of Souls + Ghost Quarter

[Maximo]

If I use {Ghost Quarter} to destroy {Cavern of Souls} in response to him casting a creature card with it, can I then counter the spell?

[BlackJester]

No, the condition is setup once the mana has been used on the creature spell.  The mana has the property regardless of the Cavern being in play.

[Coffee Vampire]

Not in response to him casting it. If he taps it for mana, he adds one uncounterable-special mana to his mana pool. Even if the cavern is destroyed, the uncounterable-special mana will still be in his mana pool to use.

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[BadLuckIrish]

Not in response to him casting it. If he taps it for mana, he adds one uncounterable-special mana to his mana pool. Even if the cavern is destroyed, the uncounterable-special mana will still be in his mana pool to use.

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+ until end of phase. Do it on ur turn itll be useless without flash

[Sagemaster]

What if he ghost quarters in response to the cavern being tapped for mana? Would that prevent the mana from being added to the pool?

[Poof]

Mana tapping doesn't use the stack
It can't be responded to

[Sagemaster]

Oh okay..my friend did something in response to me tapping for mana before     -_- I don't remember what it was but I'm pretty sure it won him the game

[Lespend]

{mana short} would be the only card that comes to mind that is a response to mana tapping... I'm sure there are others

[Poof]

It still doesn't prevent a player from tapping the mana himself to cast something

[Coffee Vampire]

I don't think you can cast that as a response to someone tapping mana...it is still just a normal instant. You can do it after someone taps mana and in response to someone trying to use it to cast a spell, but not in response to someone tapping.

[Lespend]

I guess you could cast it as someone tapped the mana to put it into his pool

[Poof]

If he's tapping mana he probably has priorty u can't cast your instant until he cast something it's on the stack already so responding with that would only tap out the lands he didn't use and he could still tap those himself and use an instant before that spell takes effect.