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How can I play Alien Swarm with only one friend and have the AI control the other two characters?

I find it very difficult to play with only 2 characters, and I'd like to fill the empty slots with AI.

I know it must be possible somehow.

EDIT: The accepted answer works, but the bots don't do anything more than firing (no healing, no welding, nothing). I have to control them to do anything more than just firing.

Does anybody know how to solve this?

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I've been doing Alien Swarm with one friend -- just he (low level techie: prototype, ammo and welder) and me (mid level medic: flamethrower, healgun and armor). Very doable and fun on easy. – badp Jul 23 '10 at 12:54
up vote 16 down vote accepted

To add a bot to your game: cl_selectm (marinenum) (slot)

To remove a bot from your game: cl_dselectm (marinenum)

(marinenum) should be between 0-7 and corresponds to the character to be added.

(slot) should be between 0-3 and relates to the player slot the bot will fill. -1 can also be used; this will fill the next available slot.

These commands must be used while in the lobby; using them anywhere else will result in invalid command errors.

Source/More information

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Great! Do you know what happens if a friend connects while the game is in progress? Will he be able to control one of the AI bots? – juanformoso Jul 23 '10 at 13:38
Yes, these buttons still work. – badp Jul 23 '10 at 13:58
@Juan Manuel It's hard for me to be certain given the game's immaturity, but I don't think it's possible to resolve your issue. Given that the game is open source, somebody may see fit to augment the default AI. If it's important to you, perhaps you could search for an emergent Alien Swarm developer community and ask there. – Lee Jul 28 '10 at 1:00

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