Hey guys...

...Hastur creature "Stealthy Byakhee" says: "After Stealthy Byakhee commits to a story, choose an opponent's character with an (Arcane) icon. That character cannot commit to the same story as Stealthy Byakhee."

This seems easy to understand when you (Hastur player) are attacking....you send in the Byakhee...and then choose a given character with Arcane and he cannot join (oppose) you at that same story. Easy in that respect.

How does it change, however, when your opponent is on the attack...and sends in a character, with Arcane icon(s) on them, and you elect to commit the Stealthy B. to that same story to oppose them ?

Do you STILL get to select and "repel" that character...because they have Arcane icons....or can you not use the S.B.'s ability "while on Defense" ?

No, works only on defense. It can't uncommit already committed characters.

Stealthy byakhee is a good card when you are the active player. You attack a story, and says this defender will not come in the story.

When you are the defender is not very useful but you can use sometime its response. Take the combo Byakhee + Polar fog for example. Your opponent attacks in story A and B, you commit your byakhee in defense (story A), say this character in the story B cannot commit in the byakhee story (cannot is an absolute world, see faq). Then, you play the Polar fog on a character in story B. It means this character have no choice, he can't go in the Byakhee story and must go in the third story.

Polar Fog
[Neutral] Mountains of Madness F19 / Illustrator: Leonardo Borazio
[Event] - Polar.
Cost : 2
Game Text: Play during your opponent's turn. Action: Choose a character committed to a story. Remove that character from that story. Then, that character's controller must commit it to a different story, if able.