Left 4 Dead: Zombies

Round-based Zombies inside Left 4 Dead 2, for up to 4 players in co-op against the game.

Survive numbered rounds on the Bus Depot. Every hit and kill pays points, and points buy Perk-a-Cola and spins of the Mystery Box. Zombies drop Max Ammo, Insta-Kill, Double Points and Nuke, and every fifth round Left 4 Dead 2's own special infected come for you instead.

Black Ops II brings its zombie bodies and voices, round music, Perk-a-Cola machines and jingles, Mystery Box and announcer. All of it is read from your own copy when Melty sets the mashup up, so you need both games installed.

The pack Melty builds stays in Left 4 Dead 2's addons folder. While it is there, Left 4 Dead 2's Commentary mode plays Black Ops II sounds instead of Valve's voices. Nothing else in the normal game changes.

Join through the game: everyone installs this from Melty and presses Play. The host then picks Exit to Main Menu, opens Mutation > Change Mutation, selects Left 4 Dead: Zombies, picks Play With Friends > Create New Left 4 Dead: Zombies Lobby, sets Server Type to Local Server, picks Create Lobby and invites friends through Steam.

Hosting through that lobby is tested, but a friend joining has not been tried yet, so co-op may need a fix once two players try it.