On the card, it reads:

"knelt, as a participant on your side in ANY challenge... etc." Here, what does 'any challenge' mean anyway? Because this wolf only has one icon, which is military, I don't see any other challenge he can participate. Or do I get it wrong?

ktei2008 said:

You got that part wrong.

Having the appropriate challenge icon only matters when you are declaring the character as an attacker or defender. Here, you are not declaring the Guardian Wolf as an attacker or a defender. You are using a card effect to bring it out of Shadows, directly into the current challenge. The only thing that matters is that there is a challenge going on, you are the attacking or defending player, and you already have a Lord or Lady participating (if I remember the text on the card correctly). The icons on the Guardian Wolf have no bearing on the use of the ability.

ktei2008 said:

The "classic" usage of this card is to jump an attacker with the Deadly keyword into the challenge as an attacker after the defending player has already committed his defenders. You get to ensure the death of a participating defender this way, especially if you jump him into an INT or POW challenge (see above). And you can do this even if you brought another card out of Shadows at the beginning of the phase. Combo that with Sister of Truth to keep returning the wolf to Shadows....

ktei2008 said:

The Card says: "Challenges: Pay the rest of Guardian Wolf's cost to bring it out of Shadows, knelt, as a participant on your side in any challenge in which you control at least 1 participating Lord or Lady character."

This means that when you bring Guardian Wolf out of Shadows during a challenge, it can participate in ANY challenge (Military, Intrigue, or Power).

If Guardian Wolf is ALREADY out, it only participates in military challenges, as per its icon.

Wow, very very professional. And, as you said, combo it with Sister of truth... I've never come up with such combo, brilliant. Thank you for your help. Gotta give a shot this week!!