Today's patch has enabled the addition of CPU dragons in multiplayer games!
The games still require at least 2 human players. Any extra player slots (determined by map) will be filled with random CPU personalities upon game launch.
This should enable you to play any map, as long as you can get at least 1 other player! And the 4-player achievements are earnable this way as well.
Please report any bugs to the Official HOARD Support forum