More than four Heroes at a time... (6+ players)

[Daedalus]

If extra-tough Quests like those in the EQP and BQP are up, then adding an extra Hero is fine, of course. But what of other Quests? Stoner81 and lestodante both mentioned adding in extra Zargon turns, which is great for keeping game length more manageable. Adding extra monsters works, but it makes a longer game and requires a sense of balance that relies on experience. If the guess is off, there is a temptation to add monsters on the fly. This would be bad in my opinion; the Heroes' actions lose meaning when Morcar/Zargon fudges the Quest no matter the Heroes' choose to do.

Here is my solution for balancing from 1 to 8 Heroes for any Quest that relies on maintaining one Morcar/Zargon turn for every four Hero turns, regardless of the number of Heroes:

Order of Play
Play begins with the Hero seated to Morcar/Zargon's left and continues clockwise. After the Hero(es)¹ have completed four turns (skipping M/Z's turn should it come up), it is M/Z's turn. On his turn, M/Z may move all monsters currently on the gameboard. Then the order begins anew, continuing clockwise from the last Hero¹ to have had a turn. This sequence continues until the Quest is achieved or until the Heroes leave the underworld.

With games of just 1 or 2 Heroes, movement should be limited each turn to one red die per Hero while any monsters are on the gameboard.

For groups of 1 to 3 Heroes, one Potion of Healing may be drawn from the Treasure Cards before the Quest for each lacking Hero. These special draws may not be kept between Quests and are returned to the Treasure Card deck when used. (Potion of Healing Treasure Cards drawn in-game are discarded as usual.)

For groups of 5 or more Heroes, remove 1 Potion of Healing from the Treasure Cards for each extra Hero.² Remove combinations pairs of other potions after that. Extra Mercenaries remove half as many potions.

1 If any Mercenaries are used, count each as having its own turn, though they are still played after the controlling Hero.
2 A standard Treasure Card deck effectively limits the total possible number of Heroes to 8, though expansions could increase this number.