Ruling Golduck is tricky...

[green_monkey]

If you use Golducks attack Encore and choose and attack that says ------- can't use this attack next turn- what happens...confused? ok example

GOLDUCKS ATTACK: Encore (20) Choose 1 of the Defending Pokemon's attacks. That Pokemon can use only that attack during your opponent's next turn.

Dialga's attack: Metal Flash (80) During your next turn, Dialga can't use Metal Flash.

 

[Bulbasaur45S]

You can't attack.

 

[DawnOfXatu]

^Yeah
I can see where you'd be confused but using an attack on a pokemon doesn't change any of the effects already on the card. (except for certain cases but this isn't one of them

 

[DukeFireBird]

you can force the encore, `the Dialga would not be able to attack you if you did that