Question re Arya's ability:

Any phase: Kneel 1 influence to choose a character with stealth or renown. Until the end of the phase, that character loses those keywords, and Arya Stark gains any keyword that was lost in this way.

If my opponent is Martell, declares a challenge and kneels Lost Oasis

The character chosen for Lost Oasis's effect already has Stealth

Challenges: Kneel Lost Oasis to choose a House Martell character. Until the end of the phase, that character gains Stealth and "after this character bypasses a character by using Stealth, kneel that character."

If I trigger Arya, does Arya cause a character to lose all instances of Stealth and Renown and is this a constant affect?

The character loses one instance of Stealth and Renown.

Khudzlin - but if you have another influence available, couldn't you then kneel it to steal any add'l stealth and renown from the same character? In fact, can't you do this as often as you want (until you can no longer pay the cost) during the player action window prior to stealth being declared?

I don't see any reason why Arya couldn't be used multiple times in order to remove all instances of those keywords. The only time she couldn't be used is when the character is absent of BOTH of those keywords.

As Bomb said, you could do it multiple times. We've established that keywords behave in a cumulative manner similar to Strength. So:

Base Stealth: 1

Lost Oasis: +1 Stealth = 2 Stealth

Arya: -1 Stealth = 1 Stealth

Arya: -1 Stealth = 0 Stealth

Two triggers of Arya would negate the stealth on a card with innate Stealth and a single, gained Stealth instance.

Yes, you can use Arya multiple times. The question was about one use.

thanks - It didn't occur to me that you could trigger Arya multiple times - that could be useful

My memory's gone fuzzy as to when you lose just one instance of an icon/keyword and when you lose all instances

Accepting that you can have multiple instances of a keyword, I take it that those only provide protection against losing them - i.e. you cannot claim double renown, count double deadly or apply double stealth

thanks - It didn't occur to me that you could trigger Arya multiple times - that could be useful

My memory's gone fuzzy as to when you lose just one instance of an icon/keyword and when you lose all instances

Accepting that you can have multiple instances of a keyword, I take it that those only provide protection against losing them - i.e. you cannot claim double renown, count double deadly or apply double stealth

Correct. Renown, deadly etc does NOT stack

My memory's gone fuzzy as to when you lose just one instance of an icon/keyword and when you lose all instances

Unless a card specifically says that you lose "all instances" of an icon/keyword, you only lose one. So 99.999% of the time, you only lose one.

Accepting that you can have multiple instances of a keyword, I take it that those only provide protection against losing them - i.e. you cannot claim double renown, count double deadly or apply double stealth

Correct. Renown, deadly etc does NOT stack

It's probably important to understand why , though. Pretty much all keywords resolve in a "character with" the keyword fashion. "For each attacking character with stealth" you get to choose one character that cannot defend. "Each participating character with renown" claims 1 power when you win a challenge. If, as the attacker, you have "more participating characters with deadly," a participating defender dies. And so on. So, it doesn't matter how many instances of stealth, renown, deadly, etc., a character may have because the multiple instances of a single keyword will never turn a single character into multiple characters.