Curbed Player Count Difficulty

You should definitely curb the difficulty depending on the player count, so 4 or 6 players have as good of a chance as 10.

Easy way to do it is by an upgrade with percentage damage/life changes.

I do it differently, since I have internal control over damage dealt and max life. Believe it or not, the game's damage and max life already scale to player count. :p

I am trying to balance it to 4 players as well, though. OD is a tough beast to balance, just be patient. :)