Starting a custom game with 0, 1 or 2 human players will give two humans. (Starting with 3 humans starts with the expected number of players.)

Seems to be an issue of limiting players to 2 instead of cults, in CustomMenu.hx it should be probably:

  if (dif.numPlayers < 1)
    dif.numPlayers = 1;
  if (dif.numCults < 2)
    dif.numCults = 2;  

Yep, it should be the other way around, 1 player and 2 cults minimum. Thanks, I uploaded the fixed version.

On a side note, it was much easier to learn haxe and find the bug than to win two times on hard settings. Thanks for the great game! :)

You're welcome! Myself, I prefer normal difficulty :)