Re: Ruling Question: Can you stop a spell by untapping the land used for it?

same thing.

Also, you seem to be talking about playing a Creeping
Mold in response to something.  Creeping Mold is a Sorcery and thus
can't
be played while anything is on the stack waiting to resolve.


Your question reveals both a lack of understanding of how spells are
paid for and also a lack of understanding of basic timing.  When you
tap a land for a spell, what you are actually doing is tapping a land
to put a point of the appropriate mana in your mana pool.  Once you have
done this, there is no further relationship between the mana point and
the
land; what happens to the land at this point is irrelevant.  Untapping
the land does not cause the mana point to be "sucked back" (in fact
the land's controller can then tap it again to get *another* point of
mana) nor does destroying the land cause the mana point to be
"destroyed".
The mana point is still in your mana pool and can be used to cast a
spell.


As concerning timing; costs, including mana costs, are paid when the
spell
is played, not when it resolves.  That means when you "respond" to a
spell
(i.e., you play a spell or effect while the original spell is still on
the
stack waiting to be resolved), the costs have *already been paid, and
are
over and done with*.  You cannot "undo" the paying of the cost.


Cheers,
Patrick