I've been asked these questions a few times at Prereleases and I hope my answers are correct. I can't see any backing from the JAR or MTR for my decision, though.

A player pays the correct amount and type of mana for a spell or activated ability. The spell has resolved. They realize that they should have tapped a different mana source in order to have the right color to cast another spell or activate another ability. At Regular REL, do we allow them to take back the payment and pay differently? I have ruled that they cannot change the payment.

My second question is related. What about if the spell or ability is still on the stack? They've cast it or activated it, they have tapped mana sources, but then realize they want to keep a certain mana source untapped for something later. If it's still on the stack and the opponent has NOT had a chance to respond, I let them change the payment. If they the opponent HAS had a chance to respond (even if the opponent did nothing), I rule they cannot change the payment.

Remember that in both cases, the original payment is legal, but it's just sub-optimal for their turn strategy. Am I ruling these correctly at Regular REL?

Your stance is how I generally handle it, Roger - though there are plenty of cases I've seen from a distance (or been a participatory member!) where the opponent allows the player to fix their mana payment.

The only time I step in and say “No, you can't do that” is if I am specifically called about the issue.

Edited Rebecca Lawrence (March 13, 2015 12:40:28 PM)

I agree with Nathaniel here. The only difference I tend to have is that I don't separate “on the stack” versus “resolved” as the line between “you can change” and “you can't”. My line more depends on what's happened since payment.

For example - if I'm tapped out and my opponent casts something, I'll usually let them change up until the end of the turn, or until they do something like draw cards which may change what they need. If they've cast something and, as I'm thinking, they change their mind, I'll probably allow it in most cases. Cases where I wouldn't would be if the change in mana changes my decision. As you can see it's pretty woolly.

Ultimately, the decision you're faced with is “are they just correcting a brain fart or not”.

In every instance, I'll make a point to suggest they take more care in future, just in case it's a competitive event.

And as Nathaniel said, if a player calls me because he doesn't want to allow a take back, I'll tend to disallow the take back. (unless it was something like “I'll cast Wrath with this, no wait, this mana”)

In regular REL I feel it's fine for mana to be changed as long as the player isn't intentionally waiting for a response and as long as another game action hasn't taken place. Regular REL is about learning and playing the game rather than competition. I also apply the same logic for playing cards and taking back the play. I know that I've played things in haste on a friday night and thought “man, that's a terrible play” immediately after putting the card down. If an opponent calls me on it then I fall back on the rules, but that hasn't happened yet. Again, just watch for reactant changing of the mind, namely AP focusing on NAP reaction before changing his mind.

If I can aggregate all of your responses, it seems like the decision to let the mana payment stand or not is whether the opponent agrees it can. I imagine the opponent will let the mana payment change if he or she is a) a good character or b) not affected negatively in either case. I will take all of your comments into consideration then next time this crops up. Thank you!