Twilight, Doors and Gates

[Snoof]

I'm sure this question has been asked many times before, but I couldn't find an answer, so here goes:

Gates of Morning cancels hazard environment effects. Is this a once off when it first comes in to play, or is it a permanent block against hazard environment effects? If so, can Twilight get rid of it? What about bringing Doors of Night into play?

Same deal with Doors of Night - one off cancellation or permanent nullification, and can Twilight or Gates of Morning get rid of it?

[Sauron]

Once GoM is in play, you may indeed use twilight or play DoN to cancel GoM.

Once DoN is in play, you may indeed use twilight or play GoM to cancel DoN.

[Snoof]

What about the cancelling effect, though? Can I bring, say, Stench of Mordor into play if Gates of Morning is in play, and does it do anything if I do?

[Bandobras Took]

The canceling/discarding occurs when the card play action of Gates resolves. It is not a continuous effect.

You may play hazard environment cards that do not required Doors of Night to be played, and such cards can take effect.

[Sauron]

The canceling/discarding occurs when the card play action of Gates resolves. It is not a continuous effect.

You may play hazard environment cards that do not required Doors of Night to be played, and such cards can take effect.

^^ What he said