Priority

[TreeTopSky]

{Curse of Echoes} is enchanted on opponent, when he casts an instant/sorcery, when do I gain priority to copy it and choose new targets for the copy?

ie: both at 5 hp, He casts {Lava Axe} on me, can i copy it and deal 5 damage to him? Furthermore, can he counter the copy?

[Giggle the Draco Genius]

When they cast a spell it will basically add a trigger to the stack that when that resolves you get to answer the question.

"Do you want to copy this spell?"  If you answer yes the copy is added to the stack and you pick targets when that happens.

[MisterJH]

When he casts it while its on te stack wouldnt you get the choice to copy and place yours on top of his? Or does it have to resolve first?

[TreeTopSky]

But when I copy it and choose to deal 5 damage to my opponent, can he cast {Counterspell} on the copy?

[TreeTopSky]

Bump, very important dispute! Thanks aswell.

[Giggle the Draco Genius]

Yes he can counter it, although you will get a chance to copy his counter and counter his counter with your counter so you can counter while you counter.

And you will be placing it above his on the stack since the only way for yours to go into the stack is if his has already been cast and went into the stack for the copy to happen in the first place.

[Pleeb]

Yes, he can counter spell it. Of course counter spell is an instant and you can then feel free to counter spell his counter spell

[TreeTopSky]

As confusing as that was, i understood it, thanks. P.S. I love my deck.

[FustyDavorite]

Counter