We are having a tournament of Hand of the King this weekend and we don't know exactly how to solve these two points:

1. If we attack a rival Hand directly, as we can target her with one of the three challange, is she considered a participating character?

I copy the relevant rules here:

"During the challenge phase, a player may initiate 1 of his 3
challenges against his opponent’s Hand of the King, if the
opponent’s Hand of the King is in play. This is announced
when the player declares the challenge. An attacked Hand
of the King automatically counts its STR during challenges
initiated against it (even if it is knelt); other eligible characters
may also be declared as defenders."

I don't know if "automatically counts its STR" means participating, as we don't declare her as a defender. It's important for some mechanics, Deadly, for example, or the new Barristan, who becomes a hand-killer.

2. The effect of removing a gold token when a Hand leaves play, is a replacement effect? Does it prevent from diying or being discarded?

I copy:

"When in play, a Hand of the King can be used as a character
by its controller, to attack, defend, and use card effects. Any effect that would cause the Hand of the King to leave play
or change control instead removes one gold token from it."

I don't know if this "instead removes one gold token" means the Hand really does'nt dye, and we can't trigger the response from Lucas, for example.

1. Yes, the Hand is participating. So you should choose one with deadly.

2. No. You are correct it is a replacement effect, but wrong about what it is replacing. That gold is being taken off after the hand is killed, discarded, returned to hand, shuffled into deck, or anything else that would make them leave play. It is a replacement effect that is changing what is happening as a result of being killed. So instead of being "killed:moribund dead pile" or "discarded:moribund discard pule" its "killed:remove a gold token." Know what I mean? So you can still trigger Lucas's effect, or Jon Arryns. I love the format, and I wrote a pretty decent (in my opinion) article of my groups Hand of the King tourney from the spring.

Best of luck. Burn is always a solid choice in this format, since it strips all the gold off the Hand until they leave play.

Thanks Mathias, very clear explanation.

In fact I'm the guy who asked you to translate your article for my blog(remember?). You can check the comments from readers on it, if you wish: ciudadeladeantigua.blogspot.com/

I don't speak spanish, so I will assume they are all good things