1) Is the purpose of Fog Cloud to make missile weapons (totally) ineffective, so the Sirine can creep up on you and use the Touch of Tranquility?
It's more of a general distraction on the Sirines' part. As long as the victim remains in the Fog Cloud it gets hit by a blindness effect every round. The blindness wears off after the victim runs out of the Fog Cloud. OTOH, Sirines mainly try to use their use Touch of Tranquility on low AC characters and spellcasters, regardless whether they are in the Fog Cloud or not.
Will the blindness effect give the normal effects of blindness, i.e. a substantial malus to
THAC0? The description doesn't seem to imply that ("The fog obscures all sight [...] beyond 2 feet"), as two feet should be enough to engage in melee.
I think so, yes. The original implementation is a bit clunky and I'll probably handle it differently in PnP Ooze creatures.
If you're interested, I was thinking of having the effect applied as a disease which deals 4 points of damage per second (up to 96 points in total) but allows the victim a window of 4 rounds to receive a Cure Disease spell before dying. Also, this attack would be suicidal for the Green Slime, unless the victim dies, in which case two new slimes pop out of its body.
Handling it differently sounds great

I like the effect, but does death happen no matter if you survive the 96 damage or not (in other words, unless you've got Cure Disease you're toast after one failed save)? That's a quite bit harsher than
PnP where you can scrape or burn the slime off. Not sure how to emulate that.. maybe allow a saving throw every round (4) until death? If you make the saving throw the ongoing damage also cease.
Love the detail about two new slimes!
Edited by Dakk, 15 January 2012 - 12:52 PM.