i was just wondering what is different when playing a three players games, which rules change?

Lighteens said:

The rules are exactly the same in a 3-player game. No changes are needed. You have 2 map tiles per player (plus home realm tiles), so the map will be a little bigger than 2 player and a little smaller than 3 player, but there's no reason to change anything else.

Keep in mind, the "Good" factions are not allies, nor are the "Evil" factions. It's always a free-for-all.