You are the judge at FNM and you are called over to a match.
Player A cast Duneblast and looks at player N. player N says “oh man, OK. choose a creature.” Player A says OK and says “i'll choose this morph, and i'll regenerate my Kin-tree warden.” Player N says that it's too late to regenerate because the duneblast is already resolving. Player A says that he thinks the Duneblast is still on the stack and he has to choose a creature before it resolves.
What do you do?

At regular I'd use this as an example on how the stack works and Allow the reginaration occur. I'd then explain to player A how resolution of spells works, and remind them to play more carefully.

Metyko is right.
Explain players that at regular REL we are lenient with mistakes (as long as they are not intentional), the main purpose of the event is to educate players and have fun.
Explain them what would happen in a Competitive REL event for purposes of education (the player casting Duneblast wouldn't have the opportunity to regenerate the creature).

I would rule that Duneblast is resolving and player A doesn't have priority to regenerate his creature. His Warden is going into the graveyard.

Since player A looked at player B after casting Duneblast to check if he had a response or not, he involuntarily passed priority. Player B asked what his choice for Duneblast was and as a result, that spell is now resolving. I would explain to player A that he needed to retain priority if he wanted to regenerate his creature immediately after casting Duneblast.

Edit - post deleted as it became irrelevant pretty quickly ;) (and I don't seem to have the power to delete my own posts)

Edited Mark Mc Govern (Jan. 9, 2015 07:04:31 PM)

Please note that I deleted my previous message because I misread an important part of the scenario. I'm making this post now just in case anybody is following this thread by email and is confused by what I said.

Thanks.


Abe

I think at FNM this is a great example to educate the players on when decisions are made. Let them regen their guy and explain that it would be very different at a bigger event (comprel).

I would also favour a lenient and educative approach here. I'd explain to the player about priority and about the correct resolution of the spell, and I would allow him to regenerate his creature.

I think even at Competitive REL, I would allow out-of-order sequencing to apply and Player A to have both the chosen creature and the regenerated creature.

But as others have said, at Regular REL, it's best to educate that the right way would be for him to regenerate before resolving Duneblast, and that choosing a creature would only happen as Duneblast is resolving.

Originally posted by Raoul Mowatt:

I think even at Competitive REL, I would allow out-of-order sequencing to apply and Player A to have both the chosen creature and the regenerated.

Generally speaking, OOoS applies if Player A were to take all the actions as a “block”, just in the wrong order, and Player A doesn't prematurely gain information that could reasonably affect later decisions in that “block”.

Player B's lack of response is pretty significant here; it lets Player A have information about what to choose and whether to regenerate the creature. That's a lot of information to affect two very big decisions. Plus, these actions don't seem reasonable to conclude as part of a “block”, not when Player A stops and looks at Player B, as if for a response (getting none and then taking other actions). That indicates a very probable pass of priority, with no real “block” of actions.

I feel that applying OOoS here is a stretch of that policy, given the description of events in the OP.

I agree with Brian. An OOoS on this would sound more like “I'll cast Duneblast choosing to keep this creature and regenerating my Kin-Tree.” That's a block of actions being done in the incorrect order, but it can be readily clarified what is going on.