Undead Nightmare

Unreleased The  Pack is an upcoming piece of downloadable content for Red Dead Redemption. The release date has not yet been announced.

The pack will include:
 * New single player missions and challenges
 * 8 new multiplayer zombie characters
 * Additional animals unleashed in the world (such as the Dead Horse)
 * New dynamic events
 * Pricing: $9.99 (PlayStation Network), 800 Microsoft Points (Xbox LIVE)

Spoilers
A leaked screen-cap of this release indicates that possibly Uncle is back: