A while ago I played through the EU base set and Kellar's Keep with only one opponent (controlling all the Heroes). It was all by-the-book playing--very few embellishments.
We found that large numbers of monsters could be quite tedious to churn through, especially in KK, which is stuffed to bursting with green things. Even though some Heroes could attack with four dice, they could still only hit one monster at a time.
We came up with a simple rule: if a Hero scores so many unblocked skulls that a monster loses more Body points than it actually has, the Heroe's attack is so powerful that the 'spare' skulls can be passed on to any other monster adjacent to the Hero.
This represents those over-the-top Conan moments when a surrounded Hero becomes a whirlwind of death slicing through several foes with a single blow. (OK, maybe not seven, but I couldn't resist the fairytale reference...)
Example: The Barbarian is flanked by two Skellies with 1BP each. He attacks a Skellie with three dice and scores three skulls. The Skellie manages to roll one black shield, so loses 2BP. Since it only has 1BP to lose, the sword chops straight through it and swings around to hit the other Skellie with the unused skull.
This helps speed up the game whenever there are lots of monsters about. Apparently there's a similar mechanic in Warhammer Quest called 'deathblow'.
You could make this an earned ability. For instance, the EU game says the Heroes become Champions after three quests but don't receive any reward (apparently there was one in the 1st edition though). Maybe becoming a Champion means you're experienced enough to use this ability. Or maybe that's too soon--maybe you earn it after completing all the quests in the base game. What do you reckon?
EDIT: Eek, a Goblin just appeared on my sidebar. I don't remember drawing a wandering monster card...