Misplay reconciling issues

[Kayle]

Okay, the topic title is totally wrong, but I'm not sure what to call it. Anyway, I've never been quite sure how this is ruled.

If player A has (for the pure sake of example) Glaceon MD #5 active, with a Water Energy and an Upper Energy attached to it, and doesn't realize that his Upper Energy isn't active or something, and declares that he is going to use Speed Slide. He only has two energy attached (WC) but the attack costs three (WCC).

- If player A announces the attack, but then in the process of resolving the attack or before resolving, he realizes he can't actually use Speed Slide, can he switch his move to Snow Cloak, or is he stuck ending his turn because of an invalid move?
- If player B notices that he can't use Speed Slide first and points this out, does the situation change at all?

I understand you guys don't want to get into the whole judging-ruling thing, so I'm just going to stop there. I'm not sure if this is a kind of question you like answering either but I figured I'd try. Thanks.

[PokePop]

This is actually a situation that POP has ruled on, so we can give a definitive answer.

The player is in the attack part of the turn.
They can't go back (without their opponent's approval, anyway) and play any additional cards or use any additional effects that would then allow the use of the attack that they were trying to use.

So, can they do a different attack or are they stuck just ending their turn?

Yes, they can choose a different attack that is available to that Pokemon, if a legal one is available, and do that attack, or choose to just pass if they don't want to do the other attack.

If there is no attack that they can legally do, then they have to end their turn without attacking.

This is a ruling from POP and so should not be variable depending on which judge you happen to get.