Iron Man mode should be more challenging for players.
Bandits - more in party, stronger opponents, more spawns, more aggressive, perhaps raid villages?
Enemy Vassels - aggressive, often no mercy, stronger etc.
Weather effects - affects the world map, affects everyone's skills, random weather events, (sandstorms - your party got lost in the sandstorm - lose 10 men, for example)
Random events - players would come across random events that players would sometimes need to make a decision, for example, you come across a group of bandits that are demanding a toll to enter their territory, either pay or fight (your money or your life). Of course the price would be high. Or no choice events, players don't have a choice, since it just happened, for example, your party were affected by a plague - lose 10 men
These are some of things that I just thought, but I'm sure there are more. Shall we discuss more ideas?