We have the following situation:

Anton controls a Weldfast Engineer, a Heart of Kiran and a Sky Skiff. Nina has a Fatal Push in her hand.
Anton crews the Heart in his 1st Main Phase.
Anton: “Combat?”
Nena: “Okay. In your BoC Push at the Heart.”
Anton: “In Response crew Sky Skiff with the Heart.”
Nena: “Okay. Push resolves?”
Anton: “Yes. After Push resolved I have the Engineer Trigger with Sky Skiff as the target.”

—–
Anton announced the trigger after any NAP actions resolved. The update on the shortcut does not describe what the legal targets are if you announce a trigger that requires a target. There is no line limiting the possible legal targets to those that would have been legal at the beginning of BoC, so according to the new wording of the shortcut it should be okay, right?

No. This is not a legal series of actions because the Weldfast Engineer trigger may only target Artifact Creatures. Legality of targets is checked twice: when the trigger goes on the stack, and again as it is about to resolve. Since Sky Skiff was not an Artifact Creature when the trigger went on the stack, it is not a legal target for that trigger.

(I am also potentially willing to argue that the trigger was missed when AP took a game action in BoC without announcing the target…but I'm on mobile right now, so I'd rather not get into that.)

“Beginning of combat triggered abilities (even ones that target) may be announced after any non-active player action has resolved.”
He announced the trigger right after the NAP action resolved, so there should be no possibility for it being missed.

I also got a “This is fine. NAP jumped the gun.” from Toby, so I am a bit confused now :|

I find this a bit of a gotcha, but under the literal wording, I can't find
anything wrong with it. The idea apparently is that since there is an
opportunity now for NAP to pass and see what AP does in BOC, he or she
needs to do so in order to prevent such an occurrence. So what NAP needs to
do is:

Anton controls a Weldfast Engineer, a Heart of Kiran and a Sky Skiff. Nina
has a Fatal Push in her hand.
Anton crews the Heart in his 1st Main Phase.
Anton: “Combat?”
Nena: “Okay.“
Anton: “I have the Engineer Trigger with Heart of Kiran as the target.” (He
can't target Sky Skiff as it is not a creature yet.)
Nena: ”Push at the Heart in response.“
Anton: ”Crew the Sky Skiff with the Heart of Kiran."

I'm not entirely clear which part you're disagreeing with - I'm happy to close this and ask for an ‘O’, but I want to make sure I know what we're asking for. Are you claiming that Toby stated that it is OK for AP to target the Sky Skiff in this scenario, or it is OK for AP to still announce the Weldfast Engineer trigger after AP has taken an action (crewing Sky Skiff) in BoC?

Edit: To be clear, my question is to Maximilian

Edited Dan Collins (May 3, 2017 12:57:11 PM)

If I understand Toby's answer correct, then the shortcut allows actions that would be illegal without the shortcut. The MTR takes precedence over the CR, so it could be possible that way. But the wording of the shortcut is not that clear on this topic and Toby's answer is also ambiguous.

We also got this topic at our judge conference in Frankfurt (the topic with the longest discussion) and we were not sure how it is meant, but in the end we had to stick with one interpretation.
The same goes for the part, in what situations NAP's action is still in MP1 - destroying the creature with the triggered ability vs destroying the only legal target; what if the triggered ability has an intervening if; what if NAP's action does not prevent the trigger but changes what will happen as it resolves?… - just a small part of it

Edited Maximilian Gerlach (May 3, 2017 01:15:31 PM)

OK, so the question here seems to be:

If players take actions in the Beginning of Combat step (such as AP crewing a vehicle in response to an NAP effect), and then AP must announce a Beginning of Combat triggered ability with a target (such as Weldcraft Engineer), is it legal to choose a target if that object did not exist, or would not have been a legal target for that triggered ability, if the triggered ability was placed on the stack at the correct time?

Closed for ‘O’ - Scott or Toby?

Essentially - as Dominick points out - there are better ways for NAP to handle this; as described in the original post, NAP acted a bit quickly and made it possible for AP to do something that wouldn't happen without (a) this shortcut and (b) NAP's hasty action.

And, as noted in a very similar thread - this isn't going to happen to approximately 98% of us… ;)

d:^D