My understanding of this card is to do with the difference between playing and put-into-play.
Here's what I understand should happen when the Red Viper is killed and, influence providing, this event is played. I search my deck (not dead pile, hand or discard pile) "for any number of Sand Snake characters" and I put them into play, immediately attaching any duplicates to them that remain in the deck .
I play with one or two people that object to this. They claim that duplicates can only be attached during the marshalling phase. My answer to this is that put-into-play effects bypass this normal restriction, therefore allowing immediate attachment of duplicates. I always refer to two areas in the most recent FAQ:
3.29: "You may not play, put into play, or take control of a unique card already in play that you own or control (except for putting a duplicate on a card that you own and control)..."
4.4: ""Put into Play" is a game mechanic that bypasses all costs (including all gold penalties) and play restrictions."
I'd be really grateful if someone could put this issue to bed once and for all (if only to allow my Sand Snakes their freedom!) The main issue being: can duplicates be immediately attached to Sand Snake characters put into play when this event is played?