With regards to the monster, I love it, it's creepy and used by a good GM would make me crap my pants. But I'm biased, as the designer's my brother.
Biased or not I have to mention that:
Stuffy Grammarian wrote:
A single victim is not a "them." Rather, the victim is a "he" or "she" (presumably, although an ooze victim might well be an "it").
I hate to get drawn into the grammar but as an English teacher I feel obliged to say that Daniel's usage is exactly right, "their" is the possessive pronoun used in either the plural case or instead of "his" or "her" when the sex is not known.
Please see
http://dictionary.reference.com/browse/their
or any grammar book for details.
Good luck Dan!