You don't get to look at the cards exiled with Wall of Mourning. If there are more than one, you choose which one to put back into your hand at random without looking at them. This is true even if you knew what one or more cards from the top of your library were before exiling them.
Defender
When this creature enters, exile a card from the top of your library face down for each opponent you have.
Coven — At the beginning of your end step, if you control three or more creatures with different powers, put a card exiled with this creature into its owner's hand.
