Looking at Vrock demons, it seems to me that they can pull off some pretty cheesy tactics based around their Spores ability.
So, the tactic would go like this - round 1, the Vrock moves into the center of the party, releases its spores, then teleports away. Everyone in the party takes 1d8 damage and is now taking 1d4 damage per round for the next 10 rounds. Next, the Vrock throws up a mirror image and waits 3 rounds for its spores ability to recharge. Then it teleports back, moves up to the largest concentration of PCs, and releases spores again. Next round, it teleports away again, renews its mirror image (if any images were lost), and waits 3 more rounds before starting the whole cycle over again. Since it doesn't say that a character can only be under the effect of one group of spores at a time, every 3 rounds the Vrock is effectively doing another 1d8+10d4 points of damage to whoever it can reach.
Now, it's true that there are ways to deal with the spores, but unless the party happens to be carrying 50 vials of holy water, they're limited resources that are probably going to run out very quickly. A lot more quickly than an average 9th level party could probably kill a Vrock, especially given that they can only attack it for one out of every three rounds, and they always have a fresh mirror image to deal with.
It seems to me that this tactic could easily result in a TPK for a 9th level party unless they happened to have Dimensional Anchor prepared (which is hardly standard for a party of that level IME).
The SRD said:Spores (Ex): A vrock can release masses of spores from its body once every 3 rounds as a free action. The spores automatically deal 1d8 points of damage to all creatures adjacent to the vrock. They then penetrate the skin and grow, dealing an additional 1d4 points of damage each round for 10 rounds. At the end of this time, the victim is covered with a tangle of viny growths. (The vines are harmless and wither away in 1d4 days.) A delay poison spell stops the spores’ growth for its duration. Bless, neutralize poison, or remove disease kills the spores, as does sprinkling the victim with a vial of holy water.
So, the tactic would go like this - round 1, the Vrock moves into the center of the party, releases its spores, then teleports away. Everyone in the party takes 1d8 damage and is now taking 1d4 damage per round for the next 10 rounds. Next, the Vrock throws up a mirror image and waits 3 rounds for its spores ability to recharge. Then it teleports back, moves up to the largest concentration of PCs, and releases spores again. Next round, it teleports away again, renews its mirror image (if any images were lost), and waits 3 more rounds before starting the whole cycle over again. Since it doesn't say that a character can only be under the effect of one group of spores at a time, every 3 rounds the Vrock is effectively doing another 1d8+10d4 points of damage to whoever it can reach.
Now, it's true that there are ways to deal with the spores, but unless the party happens to be carrying 50 vials of holy water, they're limited resources that are probably going to run out very quickly. A lot more quickly than an average 9th level party could probably kill a Vrock, especially given that they can only attack it for one out of every three rounds, and they always have a fresh mirror image to deal with.
It seems to me that this tactic could easily result in a TPK for a 9th level party unless they happened to have Dimensional Anchor prepared (which is hardly standard for a party of that level IME).