Hello.

We have started a new campaign in Descent. We played prologue and two scenarios.

There were Overlord and three heroes. Now we have one more player and want to play with four heroes.

How can we do that without restarting campaign?

Well just start him/her with the xp the heroes already earned up to that point, maybe next shopping event equip with better items if possible. The overlord now uses the starting monsters for 4 heroes instead of three, and draws 4 cards for his starting hand.

Next shopping event will get 5 items instead of 4 to choose from.

Seems a relatively easy fix.