I love the spooky cover.
The cursive header font is a little hard to read, in my opinion. I'd consider something with a similar personality that's a little easier to read.
Elegant way to handle sea elves.
I like the rival parties, who are a colorful mix of characters.
This whole adventure is packed.
Smart move throughout to just reference existing monsters instead of making new ones, which saved you a good amount of space and is fine -- 99% of players won't notice and most of those that do will understand.
I would love to see this revised and expanded. You've got so much going on here, I'd like to see more of everything, including what the mask actually does.
This whole thing just bursts with energy.