Wizkids Rules!

If my opponent uses Betrayal and I have Nocturne in my field would Nocturne be able to redirect Betrayal back at your opponent?

Rare Nocturne says:

While Nocturne is active, the first time your opponent uses an Action die each turn, you may redirect
the effect to another legal target.

Betrayal:

Deal 1 damage to target opponent for each character die in their Field Zone.
** If Betrayal dealt at least 2 damage, put this die in your Prep Area.

cynicalpuppy wrote:If my opponent uses Betrayal and I have Nocturne in my field would Nocturne be able to redirect Betrayal back at your opponent?

Rare Nocturne says:

While Nocturne is active, the first time your opponent uses an Action die each turn, you may redirect
the effect to another legal target.

Betrayal:

Deal 1 damage to target opponent for each character die in their Field Zone.
** If Betrayal dealt at least 2 damage, put this die in your Prep Area.

In this case, “legal target" refers to how the action die was originally played. If the action originally targeted an opposing die, Nocturne would be able to redirect it to another die opposing the player who originally used the action being redirected.

In your example, Betrayal could only be redirected to a different opponent of the player who originally played Betrayal (which doesn't exist in a normal 1 vs 1 game).