The Guardian is a move for your sandwich effects. The revelation is up to you.
Imagine, you show two black jacks face up on the top of the deck. Then you riffle through the cards and ask someone to say stop. Now the selection is lost again in the pack using the jacks.
You show the empty black jacks front and back and explain that you are going to try to catch the selection while you riffle through the deck. This is exactly what you do.
You throw the jacks face up through the deck and when you spread the pack, the spectators can see the impossible. Between the two face up cards, there is the selection.
The Guardian is a idea to put a selection in a sandwich position. The revelation is totally up to you. I hope you like it. Enjoy!