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Co-op VS

Allows you and your friends to play as infected in Co-op mode.
Works in singleplayer and local server.

Please Note: this is not a mutation, it alters the normal co-op. Disable the addon to go back to vanilla co-op.

If you have the Left 4 Fun addon you can switch team whenever you want with:
!l4f team
and you can change infected type (while in ghostmode) with:
!l4f next_infected

With Left 4 Bots 2 the bots will be able to complete the official campaigns on their own.