That could certainly work. Would a creature with fast healing still heal quickly if damaged up to -9 hp? If so, I'm OK with it then. If you actually get the moss down to -10 hp or less it should be dead, but if you just take it to just under 0 and leave it then it will come back. The fire vulnerability will help ensure that it will meet its end if you burn it.
i took the time to more thoroughly read the responses on the thread, and i have modified these attacks accordingly. responses?
"Vampiric Link" (Su): A vampire moss can drain the life from any creature within 30 feet. To do so, it must be aware of the creature and take a standard action to attempt to establish a link. The vampire moss doesn't need to touch the creature to establish a link. This is a mind-affecting effect.
The target creature will feel a prickling sensation at the back of the neck, and must succeed on a DC X Fortitude save. On a successful save, the link fails to establish, though the vampire moss may attempt again on its next turn. A failed save indicates that a supernatural link has been established.
The victim will not be automatically aware of the link, but must succeed on a DC X Will save to notice the attack. Each round the link remains entitles the creature to another Will save to notice the link, with a cumulative +2 bonus on the check per round after the first.
If its victim dies before the moss's appetite has been sated, the moss seeks a new target. If the victim moves more than 30 feet away from the feeding moss, or if the feeding moss is slain, the link is severed. The save DCs are (Constitution?)-based.
"Energy Stealing" (Ex): A vampire moss can cause persistent energy loss in a creature it has established a vampiric link with. Such a creature loses 1 hit point each round. This continuing hit point loss cannot be stopped by a Heal check, cure spell, or heal spell, though these methods can restore lost hit points. The vampire moss gains temporary hit points equal to the number of hit points lost in this way (which disappear after X days?). If the vampiric link is severed, the hit point loss ceases immediately.
If the hit point loss continues for a full minute, the victim must succeed on a DC X Fortitude save or fall unconscious (for X rounds). The save DC is (Charisma?)-based.
After a vampire moss has drained a number of hit points equal to 4 times its own maximum hit point total (X points for a typical vampire moss), it is sated and severs the vampiric link.
Kafkonia said:
Perhaps we should go by effect-on-PCs rather than trying to mimic its exact numbers. How many HP did a typical PC have when this badboy was around? I don't have my books with me.
A quick guideline to keep in mind is that 4 times the moss's hit points will be exactly the same as two full hit dice (since avg hit die = half hit die) so we might want to consider that too -- how many HD will this have? Will we still go with 1/2?
Well, back in the day it was less common for a PC to have bonus hp due to Con scores, but they were definitely still around. In fact, non-warrior types in 2E had a cap of +2 on how much of a Con bonus they could get to hp, no matter how high their Con went! So, we could assume that the average 1st-level fighter with no Con bonus (15 Con gave you +1 per HD, with roughly +1 more per HD) would have 5 hp, while you could conceivably have a guy with 1 hp, and if you had a Con of 18 the maximum hp you could get would be 14. I'd say as a rough estimate that the average hp for a 2E PC was about 3-4. so, assuming a 1st-level encounter, a vampire mist might just finish off 4 PCs by itself if it gets lucky! YMMV of course, as I'm sure different campaigns were run in different ways.
We're most likely going to go with 1-HD for the vampire moss, since 1/2 HD seems to have been all but eliminated in 3.5 (anything but the grig?) and that helps for advancement and a lot of other numbers issues anyway.