Black Betha: Response: After you win a challenge in which you have declared a attacker, kneel Black Betha to attach the top card of your discard pile face-down to a unique character as a duplicate (Limit once per round.)

Can you use this effect to dupe a character that is immune to locations, since it doesn't choose the character as a target?

Attachments, duplicates and tokens are not covered by immunity, as they are not the card itself. They can be put on or taken away without running afoul of immunity (Ellaria Sand can take power from The Red Viper). Abilities of the card (including dupe save) are not immune to anything either and can normally be cancelled.

Alando said:

Be wary though - an immune card does not have to be chosen as the target of an effect to be immune to it. Immune cards also ignore effects of the types they are immune to without being chosen as a target, as long as those effects directly interact with the immune card.

Alando said:

Not sure if their responses helped you.

The answer is yes, LoL. They gave you the reasons.