The PCs believe that infesting clath (which look like unnatural half-real one-celled creatures, roughly the size of a dog, shimmeringly translucent) have several stages.
1. Recent infestation: less powerful with no known way to attack psychically. Can be detected by the host's rainbow-sheened eyes.
2. Intermediate infestation: the rainbow-colored eyes disappear for someone whose sight isn't specially, magically enhanced. Unable to drag foes into special psychic arenas, they can fight physically in their borrowed bodies... and when those bodies die, can emerge to fight physically themselves.
3. Advanced infestation. Can drag foes away into a psychic arena for private destruction. It's unknown what happens when they defeat foes there, but taking over their physical form seems likely.
It's known that clath lay eggs, that they don't seem to be from this world, and that they are summoned by setting up mirrors inside of a witchwater tower.
In last night's combat, we had a remarkable thing: a long (2.5 hours) fight that moved pretty quickly, never dragged or became boring. We did this by starting the fight with mortal foes, 3 lvl 14 melee (a barbarian, a rogue and a cleaver-wielding cook) and 2 lvl 14 spellcasters (a wizard and a nature priest). They entered the battlefield from two sides and stayed somewhat mobile despite some great PC attempts to restrict their movement. One round after each foe died (at the monster's normal "bloodied" value), a clath emerged from it. The clath are much more mobile, tend to attack reflex, and do brutal amounts of damage when they hit. Luckily, these ones weren't as accurate as some foes the PCs have fought, and the group used excellent tactics to guard each other, separate their foes and focus fire. The PCs ended the fight with all encounters gone and almost all dailies used up. It was a nice challenge.
My conclusions from this fight:
- The warforged wizard Strontium did a great job controlling. Since she prefers direct damage spells, the player was quite chuffed about this. "See? I CAN be a controller!" This made a fair amount of difference in how many clath were attacking at once.
- With absurdly high defenses, Sagiro's rogue Cobalt has become impromptu defender. An ability to stop foes from moving played havoc, though. The shaman Bramble kept being targeted by Clath because (other than brutally slaying them with opportunity attacks!) it was difficult to stop the monsters from moving.
- Logan the avenger finally got to use his full range of powers that kick in when an enemy moves away from him. This made the mobile fight a lot more fun for all of us. I'll be doing more of this in future fights, instead of tending towards the more static foes.
- The shaman gave everyone DR5 early on. Tremendously useful.
- As a DM, scoring two crits with two successive attacks on the same PC in the same round is really, really fun. Shh, don't tell my players.