Zed's Dead, Baby

 is an achievement/trophy in the Red Dead Redemption Undead Nightmare DLC pack.

Description
"Attain 100% Game Completion statistic in Undead Nightmare." After obtaining 100% completion in Undead Nightmare, Unlimited item and ammo creation becomes available.

Undead Nightmare is significantly easier to 100% than Redemption, and can easily be done in less than 9 hours total gameplay.

Acquisition
This achievement requires players to completely finish every aspect of the game, which requires:

Complete all the missions:

 * "Curious Tales from Blackwater, USA"
 * "Paternal Pride"
 * "Dinner for Two"
 * "Get Back in That Hole, Partner"
 * "Birth of the Conservation Movement"
 * "A Cure for Most of What Ails You"
 * "Missing Souls"
 * "Filth and Other Entertainment"
 * "Biographies and Lies"
 * "Mother Superior Blues"
 * "On a Pale Horse"

Have all the regions saved at least once:
West Elizabeth
 * Blackwater
 * Manzanita Post
 * Cochinay
 * Pacific Union R.R. Camp

New Austin
 * Thieves Landing
 * MacFarlane's Ranch
 * Armadillo
 * Twin Rocks
 * Fort Mercer
 * Plainview
 * Ridgewood Farm
 * Rathskeller Fork
 * Gaptooth Breach

Nuevo Paraiso
 * Nosalida
 * Escalera
 * Tesoro Azul
 * Chuparosa
 * Las Hermanas
 * Agave Viejo
 * Casa Madrugada
 * El Presidio
 * El Matadero
 * Torquemada

Cleanse All the Graveyards:

 * 1) Blackwater Graveyard
 * 2) Coot's Chapel
 * 3) Odd Fellow's Rest
 * 4) Tumbleweed Graveyard
 * 5) Sepulcro

Save all Missing Persons

 * 10 Missing Persons in Fort Mercer
 * 6 Missing Persons in El Presidio

Break the Unicorn

 * To locate the Unicorn, The Chupacabra must first be killed. It will then be found in the same area the Hungarian Half-Bred was located.

Complete all the Challenges:

 * Four Horses of the Apocalypse
 * Undead Hunter
 * Undead Treasure Hunter
 * Undead Sharpshooter

Get all The Outfits

 * Legend of the Apocalypse/Undead
 * Undead Hunter/Army of the Undead
 * Undead Cowboy Outfit

Trivia

 * The title of this achievement/trophy is a partial quote from Butch Coolidge, a character played by Bruce Willis in the film Pulp Fiction.
 * This is also the title of a song by the band "cancer bats"