Question 1:

When I play (use) an advantage card, when and how and the ability take effect? Does the card need to remain in play to take effect?

For example, during combat, I play an advantage card (A) that gives me +3 to combat.

My opponent subsequenty uses Millenium to remove the advantage card. Do I lose the +3?

From our understanding, the advantage cards need to stay in play to take effect. Therefore, Millenium is essentially a counterspell to everything except for on-play cards then.

Also this makes Artifact: Fathum not as good. Since if I return card (A) if I roll a 6 then it bounces back to my hand and I'll lose the +3.

Question 2:

Elisabetta: Can I reroll any dice rolls in the game including other player's exploration rolls, or other player's combat rolls.

Question 3:

Cancel X. If it says cancel X, when does the target being cancelled need to be cancelled, does it need to be cancelled the immediately when the card is played or can it "disenchant" something that has been in play for a while now. There are barely any cards in the game that disenchants other cards.