I am thinking of creating a custom mission, which "plays" with a moody Gandalf. That for I need some clarification. What happens if Gandalf (hero or ally) is in play and an enemy called Gandalf gets reveald? Will the when reveald effect occur before discarding that card (because there is allready an unique card called Gandalf in play)? I hope so, otherwise my mission wont work.

A unique card can't be played and can't enter play if another one is already in play.

Encounter deck does not play any card (they are revealed or put in play, but no one never play them), so the only problematic part would be the "enter play". Since "when revealed" occur before the card enter play it seem to work as intended.

I believe that there is a "golden rule" that the card text overrides the rules. So above the "when revealed" line, include your line to Discard other gandalfs, and then move the "when revealed:" down below that.

What the point? It already work this way.

On 7/5/2018 at 6:16 PM, Rouxxor said:

Encounter  deck does not play any card (they are revealed or put in play, but no one never play them), so the only problematic part would be the "enter play". Since "when revealed" occur  before the card enter play it seem to work as intended. 

The boldfaced is actually something of an interesting point—while I thought the same way, I believe the CotR guys got a different ruling. (Yes, yes, the RR defines "in play" quite specifically, but nevertheless, looks like Caleb may have changed his mind.) Apparently Caleb is working on a FAQ revision, so hopefully it will be cleared up.

BTW, I think you don't need the When Revealed text… RR Unique Cards :

If a unique version of a character enters play from the encounter deck and there is already a copy of that character under a player’s control, that player must discard the version he or she controls.

There have been a few discrepancies among the rules, R.R, and FAQ, so we might be due for a new FAQ.