Jaldean, here's my comments on your beasties:
Assassin fly: Seemed fine, nice way of making tiny vermin nasty something to be afeared of.
Boatman: Nice idea, works pretty well, I really like the idea of being able to bargain to save yourself

SOmething I've noticed with this monster and lots of others in the book is for some odd reason Constitution-draining attacks pop up lots, and I don't like con drains very much since they tend to make the monster really lethal.
Dune prowler: Works fine, a good solid monster that isn't completely wierd and works well in its described ecological niche.
Eldritch: I like the picture

and the idea is distinct enough from other undead, but I wont be using it myself.
Lemax: I Cant remember what the lemax is
Oasis ooze: Cool idea though I'm not too sure about the rate at which it expands again if disturbed...
Rusalka: Cool creature, fills a nice 'evil fey' niche that needed doing.
Sepulcharal lurker: Love the picture, and I like the way it's a neutral nasty as well. Very cool.
Tatzylwurm: Quite a nasty beastie, somehow it's not bland despite the fact that I get the feeling it *should* be. The picture, description and similar little things just make it cool as well.