You also need the clue token effect.
This is a Alan Montgomery's idea variant:http://www.boardgamegeek.com/geekforum.php3?action=viewthrea...
At the beginnig of Mythos Phase:
1º Starting first player and clockwise order, every player roll a die. Each clue token the player spends(not another players)AFTER die roll, add +1. If the die result is 1 or 2 the player draw a Mytos card face down.
2º Starting first player and clockwise order, each player with a Mytos card reveal it.
a) for all cards excep the last: only aply the action 1 of Mytos phase "Open Gate and Spawn Monster"
b) for the last card: aply all the actions of the Mytos phase.
3º If no player rolls a 1 or 2, however draw a Mytos and aply all de actions of the Mytos Phase normally.
I had this only apply the movement effects, this is necessary so that one or two players don't get too many gates appearing.
Advantages of this variant:
There is a proportion between the actions of evil and the number of players (like in LOTR and Les Chevaliers de la Talbe Ronde)
The players confront the dilemma of spending clue tokens to avoid open new doors and more monsters appear. And to spend more clue tokens means more difficulties to seal doors...
There also need to be adjustments to the monster limits as number of monsters appearing has changed, and probably changes to the maximum number of gates.