I have a question.. Lets say if I were to attack with Korvold, Fae-Cursed King and target a treasure to sacrifice. Can I respond to Korvolds trigger while on the stack and sacrifice the targeted treasure to gain the mana, and still use korvold to attack?
You can activate an ability of the form "T, Sacrifice this artifact: Add one mana of any color" in response to Korvold's first triggered ability (C.R. 117.7, 117.1b). If you do, Korvold's last ability will trigger, then you add one mana of any color, then you put the ability that just triggered on the stack (C.R. 605.1a, 605.3b, 405.6c, 117.5).
Note that Korvold's first triggered ability is still on the stack, so that when it resolves, you must still sacrifice a permanent other than Korvold if possible. Note also that that ability doesn't target anything (it lacks the word "target", for example), so that you don't choose what to sacrifice for that ability until that ability resolves (C.R. 115.1d, 608.2d).
Finally, note that although a "Treasure token", as defined by C.R. 111.10a, is a "colorless Treasure artifact token with" the activated ability just mentioned, the Treasure artifact type itself (C.R. 205.3g) has no abilities or game mechanics inherent to that type, including that activated ability.
If Korvold's first triggered ability were to say "...sacrifice another target permanent" rather than "...sacrifice another permanent", but the targeted permanent leaves the battlefield before that ability resolves, that ability will fail to resolve and do nothing (C.R. 608.2b), but even so, this won't remove Korvold from combat (since the ability existed independently of Korvold once it triggered) (C.R. 113.7a).
I have a question.. Lets say if I were to attack with Korvold, Fae-Cursed King and target a treasure to sacrifice. Can I respond to Korvolds trigger while on the stack and sacrifice the targeted treasure to gain the mana, and still use korvold to attack?
No, that doesn't work. You'll need to sacrifice something to Korvold, and that can't be something you've already sacrificed for some other reason.
I have a question.. Lets say if I were to attack with Korvold, Fae-Cursed King and target a treasure to sacrifice. Can I respond to Korvolds trigger while on the stack and sacrifice the targeted treasure to gain the mana, and still use korvold to attack?
Note that Korvold's first triggered ability is still on the stack, so that when it resolves, you must still sacrifice a permanent other than Korvold if possible. Note also that that ability doesn't target anything (it lacks the word "target", for example), so that you don't choose what to sacrifice for that ability until that ability resolves (C.R. 115.1d, 608.2d).
Finally, note that although a "Treasure token", as defined by C.R. 111.10a, is a "colorless Treasure artifact token with" the activated ability just mentioned, the Treasure artifact type itself (C.R. 205.3g) has no abilities or game mechanics inherent to that type, including that activated ability.
If Korvold's first triggered ability were to say "...sacrifice another target permanent" rather than "...sacrifice another permanent", but the targeted permanent leaves the battlefield before that ability resolves, that ability will fail to resolve and do nothing (C.R. 608.2b), but even so, this won't remove Korvold from combat (since the ability existed independently of Korvold once it triggered) (C.R. 113.7a).
EDIT (May 24): Correction.
EDIT (Feb. 18, 2021): Correction.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules