Form 2 monster cups:
1. Regular
2. Masks (there are 10 masks with all expansions... so like a mini-cup)

Each time a gate opens, 1 monster is drawn from the regular cup and 1 from the mask cup. If there are 5 or more players, it's 2 regular monsters and 1 mask monster.

When a monster surge occurs, you take the lower number, halve it, and that many monsters are drawn from the mask cup.
Example: There are 4 open gates and 6 players. 6 monsters should appear- 2 of them from the mask cup (half of 4, the lower number)

Closing/sealing gates does not banish masks. They do count towards the monster limit though.

If a mask should be drawn but the mask cup is empty, raise the terror level by 1 for each mask that should've been drawn.

Also play with the Dark Pharaoh herald; this way, there are sure to be masks around when nyry awakens (and the herald improves his rating by -1 and adds a doom token for each mask on the board).

Discuss.

nothing? I thought it was pretty good

Try play testing it and give some statistics on how it affects the game, it may be a good idea and may be a bad one. But it is pretty hard to judge without investing alot of time playstesting it and since you came up with it you might want to play test and fine tune it before suggesting it to regular Arkham groups.

If during playtesting questions come up, like how reliant diffrent people are on certain tactics etc. thats a valid inquery and folks will respond.

Not knocking your idea, but just pointing out that if its not tested and still just in the "idea" phase you need to do some hard work before getting valid input (or have people agree to play test with you for faster information).

I think it is a good idea. Though it is similar to custom heralds (at least to the crawling chaos) that was posted some time ago.