Whisperer Encounters will have a special icon and you will have a chance to find a member of a mysterious group that wears the skins of walkers to mask their presence – Whisperers! Don't take too long slaying the Walkers, Whisperers will sneak past your companion and head straight for you.

Whisperer Encounters have much better rewards than a regular encounter - and even better rewards than Rare Encounter (which also costs 3 energy). It gives exactly the same amount of cards as Rare Encounter (with guaranteed Rare as well) and also gives a chance for Epic and Legendary cards (something that Rare Encounter doesn't). On top of all that, it gives Bow cards.