Situation 1:

Stark player defends against a challenge with Robb Stark with Seal of the Hand attached (Action: stand the character)

Targaryen player issues another challenge.

Star players stands Robb to defend against the second challenge (is this correct? Or can the Stark player only stand his characters on his own turn?)

Situation 2:

Targaryen players attacks with Areo Hotath, Stark defends with only one card. Hotah removes the defender - is the defending card still knelt? Or is treated as if it wasn't in the challenge? Is the challenge considered 'undefended' then?

Thanks!

Situation 1:

Stark player defends against a challenge with Robb Stark with Seal of the Hand attached (Action: stand the character)

Targaryen player issues another challenge.

Star players stands Robb to defend against the second challenge (is this correct? Or can the Stark player only stand his characters on his own turn?)

Situation 2:

Targaryen players attacks with Areo Hotath, Stark defends with only one card. Hotah removes the defender - is the defending card still knelt? Or is treated as if it wasn't in the challenge? Is the challenge considered 'undefended' then?

Thanks!

Situation 1: The Stark player can use "Seal of the Hand" as an action, any time player actions are possible. He does not have to wait until he's the active player. For more information on when players can take player actions, check out the timing charts on p.24-25. For the most part, it's easy: Do the thing the phase is about (e.g. plot, draw), then players can take actions. The challenges phase is a bit trickier, as there's the opportunity to take actions before the each challenge, after attackers are declared, and after defenders are declared.

Situation 2: The defending character is still knelt, as Areo's effect doesn't stand it. The challenge would be considered unopposed, as there are no longer any defenders. For effects which do otherwise, see (for instance) "Highgarden" which specifies that it stands and removes the character from the challenge.

Situation 2: The defending character is still knelt, as Areo's effect doesn't stand it. The challenge would be considered unopposed, as there are no longer any defender s . For effects which do otherwise, see (for instance) "Highgarden" which specifies that it stands and removes the character from the challenge.

Technical, but important, distinction. The challenge is considered unopposed because the defending character counts 0 total STR in the challenge, not necessarily because there are no defending characters.

(It is the count of 0 total STR in the challenge, not the number of defending characters, that makes a challenge unopposed. There can be situations where there are defending characters, but the defending player counts 0 total STR; those challenges would be considered unopposed, too.)

It can be noted that every existing bonus to challenge STR depends on the presence of at least 1 participating character. This has been consistent throughout the 1st edition LCG (possibly throughout the CCG as well), despite not being a rule (mostly because there are very few such effects; I can think of only 1 other than melee titles for each edition). So "no defending characters" does imply 0 STR, thus allowing us to make the implication of "there are no defenders, so the challenge is unopposed" (that implication isn't reversible, though, as you rightfully point out).

The distinction for 2nd edition is that the challenge doesn't "fizzle" if there are no attackers like it did in first edition.

The distinction for 2nd edition is that the challenge doesn't "fizzle" if there are no attackers like it did in first edition.

I'm not sure what this has to do with whether or not a challenge is unopposed, but in first edition, the challenge did not "fizzle" if there were no attackers. It ended without resolution if there were no participating characters . That is a huge distinction.