This one caused quite a bit of discussion a week ago and this week again (retelling the scenario) judges were divided on the subject. It comes from a real call that players made during a PTQ, so here is the scenario:

Nico controls a Grizzly Bears that he just attacked with the previous turn. Angelo no in his turn attacks with only his Perplexing Chimera. Nico plays Divine Verdict targeting the Chimera before combat damage. Angelo replies: “okay swap and retarget to the Bears”. A judge is called by both players as they together find out this retarget is not possible, they confirm the above story and they ask “how far do we return back judge?”.

I won't spoil too much already, but I would like to hear your thoughts.

I'd issue a GRV to Angelo for trying to change the target of a spell to an illegal target. I would backup to having Perplexing Chimera's trigger on the stack and have him resolve it legally. Nico - even though it says you may choose a new target for the spell, it has to be a legal target for the spell.

Edit: I meant Angelo. :) And yes, I agree the action to backup would be the second sentence of choosing a new target, not the initial trigger and choosing whether or not to use it.

Edited Brian Brown (April 21, 2014 07:28:06 AM)

Originally posted by Brian Brown:

I'd issue a GRV to Nico for trying to change the target of a spell to an illegal target. I would backup to having Perplexing Chimera's trigger on the stack and have him resolve it legally. Nico - even though it says you may choose a new target for the spell, it has to be a legal target for the spell.

Actually, Angelo has commited an infraction, not Nico (Angelo controlled Perplexing Chimera's trigger).
The real question in this scenario seems to be "Does Angelo have to change control of Perplexing Chimera and Divine Verdict, or can he choose to keep his Chimera?"
@Brian Brown: Would you rewind to the point immediately before the trigger resolves, or to the point before Angelo chooses wether to change the spell's target?

If I were to decide, I'd rewind to the point immediately prior to the error. The error itself was choosing an illegal set of targets for Divine Verdict when choosing new targets(CR 114.6d-e). Until this point, all actions have been legal, and no (game) rule tells us to return to an earlier point when rewinding the resolution of an ability.
Therefor, after the rewind, Nico controls Angelo's tapped Perplexing Chimera, and Angelo controls Nico's Divine Verdict on the stack. The next game action is choosing new targets for Divine Verdict. He does not have to change the target, even if there were other legal targets for it. If there are no other legal targets, he can't change it, and Divine Verdict will be countered on resolution because Perplexing Chimera has been removed from combat.

Changing control over Divine Verdict and Chimera was a bad, but legal action. It didn't reach the outcome he expected, but it was certainly legal and he clearly chose to swap control over those cards.

Then, a GRV occured. I'll rewind to exactly that point: N already controls Chimera, A now controls a Divine Verdict that targets his very own Bear.

I'm going with Sebastian here, the Situation might be awkward but the IPG only provides a rewind to the point immidiatly prior to the error. Exchanging Perplexing Chimera for Divine Verdict was a legal action even if Divine Verdict ends up doing nothing because of no legal target.

As someone who is learning all the tools and options a judge has its tempting to rewind right before the Perplexing Chimera changes controller and therefore fix the error of Angelo, but especially at Competitive REL i'm more confident to say that turning a incorrect game state into a correct game state should be the goal, not fixing a suboptimal decition from a player.

the Situation might be awkward

Indeed - but we've always held that rules knowledge is one of the skills that players should be able to use to their advantage. The inverse is true - lack of rules knowledge can hurt you - as it does in this example.

d:^D

Although it is awkward for Angelo, I definitely wouldn't rewind(except to say that he can't change the target to Grizzly Bears, since it isn't a legal target). He made a legal gameplay choice when he triggered Perplexing Chimera's ability. It isn't our fault that the Divine Verdict can't target anything else. Furthermore, though he may not be able to change the target of the spell(no legal targets), his actions don't change the fact that the spell is already on the stack and it had a legal target when it was cast.

Perplexing Chimera trigger resolves and Nico becomes its controller. Perplexing Chimera is removed from combat. Divine Verdict checks its target upon resolution, finds that it is no longer a valid target(no longer attacking), and is countered.

Game rules are followed, players learn how Perplexing Chimera works, and the match continues.

Depending on the exact situation, issue a GRV to Angelo for choosing an illegal target(I'm unclear on the situation as to whether or not he targeted, or simply went to target it and then realized that he couldn't).

Edited Alan Dreher (April 20, 2014 07:23:45 PM)

Thanks for the input. Interesting to see that everybody here has the same opinion. I (and some other judges) followed the path that something was wrong during the resolve and thus the whole trigger had to be resolved again, with the Nico (now realizing the technical error he made), to choose not to swap and just let his Chimera die.

After rereading the IPG on the topic I now understand what is meant by “actions” and understand that a card can have multiple actions with some of them being wrong and others not. Thanks also to Jona Bemindt and Jurgen Baert for clearing that up during the day!

What is strange though is that a handful of judges (L3 among them) went with returning up to the point in the game were the trigger of Perplexing Chimera is about to resolve. Giving me an explanation: “something went wrong during the resolve of the trigger so we going to do the whole trigger again”, much like fixing a problem during casting of a spell.

And actually thinking about it, I have a problem with it (although only a wording problem). To me when somebody casts a spell and anounces an illegal target, why do we let him redo the whole of it, because putting the spell on the stack, an action to get a spell cast to me is also “an action”. So I'm a bit puzzled with this: what is an action and what is not? or is casting a spell different in the way we resolve errors?

Edited Niki Lin (April 21, 2014 11:31:14 PM)

I give up.

Edited Aaron Huntsman (April 21, 2014 07:52:59 AM)

There actually is support in the CR for why illegal casting of spells is generally fully reversed:

717.1. If a player realizes that he or she can't legally take an action after starting to do so, the entire action is reversed and any payments already made are canceled. No abilities trigger and no effects apply as a result of an undone action. If the action was casting a spell, the spell returns to the zone it came from. The player may also reverse any legal mana abilities activated while making the illegal play, unless mana from them or from any triggered mana abilities they triggered was spent on another mana ability that wasn't reversed. Players may not reverse actions that moved cards to a library, moved cards from a library to any zone other than the stack, or caused a library to be shuffled.

This situation differs in my mind because the game action in question is legal, the player just made an illegal choice as part of resolving that action.

Originally posted by Aaron Huntsman:

If there -are- legal targets for a spell and the player chose an illegal one, you would only back up far enough to let the player choose a legal target.

No.

We do not force a player to choose a legal target in this manner.

If I target your only creature with Terror and you remind me of your creature's Hexproof, we back up the whole spell; I am not forced to choose one of my creatures, even if they're legal targets.

Originally posted by Niki Lin:

And actually thinking about it, I have a problem with it (although only a wording problem). To me when somebody casts a spell and anounces an illegal target, why do we let him redo the whole of it, because putting the spell on the stack, an action to get a spell cast to me is also “an action”. So I'm a bit puzzled with this: what is an action and what is not? or is casting a spell different in the way we resolve errors?

This threw me momentarily; the CR wording implies that the full backup only happens in case of impossibility, not just illegal choices. However it also specifically refers to the “action” of casting a spell. It's an action that has a lot of procedural steps that go with it that aren't actions in and of themselves (except for activating mana abilities) but it's still treated as one big action.

The difference in the example is that we're talking about resolving a spell, which can invoke multiple actions in sequence, and we only back up to the particular offending action.

Closer (?), but not quite.

Resolving the triggered ability of Perlexing Chimera is legal; changing the target of the spell affected by the triggered ability, in this example, is not legal.

Consider an analogous example: I attack with Humble Budoka, you block with Sylvan Caryatid; before damage, you target your Caryatid with Giant Growth. I cast Redirect, targeting your Giant Growth … and then realize I can't change the target to my (shroud-covered) Budoka. The Redirect is legal, but the result I want is not.

We don't back up the Redirect; we don't back up the Chimera's change of control.

Originally posted by Scott Marshall:

Consider an analogous example: I attack with Humble Budoka, you block with Sylvan Caryatid; before damage, you target your Caryatid with Giant Growth. I cast Redirect, targeting your Giant Growth … and then realize I can't change the target to my (shroud-covered) Budoka. The Redirect is legal, but the result I want is not.

We don't back up the Redirect; we don't back up the Chimera's change of control.

In this case, however, the illegal action was not the casting of Redirect, but how to resolve it. In-between those actions, players had priority to do other actions.

CR 717.2 would seem to imply that you reverse the illegal action(s) up to the point where the last player had priority has priority again. For the Chimera case, wouldn't that back up to before the choice of whether or not to switch control?

717.2. When reversing illegal spells and abilities, the player who had priority retains it and may take another action or pass. The player may redo the reversed action in a legal way or take any other action allowed by the rules.

As a follow-up Q, in the Budoka example, would you allow AP to cast something like Sudden Spoiling before resolving the Redirect?

I can see how reading only CR 717.2 could mislead in such a manner, but that's not the entirety of the rules regarding backing up; there's also this snippet from IPG 2.5, the Additional Remedy section:

judge may get permission from the Head Judge to back up the game to the point of the error. Each action taken is undone until the game reaches the point immediately prior to the error

Once you back up to the point of the error, the player who had priority retains it.

d:^D