This is a homebrew encounter placed at the end of The Bastards of Erebus in Palaveen's bedroom. I used it to rather good effect against my players, who now have good reason to fear the dark. Enjoy!
Ilnerik's Ink CR 6
XP 2400
NE Temporary Haunt
Caster Level 6
Notice Perception 10 (to notice the ink on the diary pages running)
HP 12; Trigger Turning to diary's blank pages Reset none
EFFECT
After getting to the end of the diary and finding blank pages Palaveen hasn't written on yet, the diary will begin to drip ink onto the floor. The ink does not come from the written pages, but from some unseen source in the diary. If the diary is damaged, the book will "bleed", pouring more ink onto the floor.
If the book is undamaged, and after five rounds of dripping ink (two if the diary is damaged), the pool of ink will rise, releasing a swarm of bats (as Bat Swarm, Bestiary pg. 30) seemingly made out of ink. These bats (who have separate initiatives than the ink pool) will not attack the PCs, but rather fly directly into any and all light sources, destroying themselves, but reducing the light level in the room by one step. These bats may be destroyed by physical attacks (swarm rules apply); if the first swarm is slain before attacking the light sources, the pool of ink will release one (and only one) more bat swarm on its next turn.
After summoning the bat swarm(s), the ink pool will produce two shadowgarms (Bastards of Erebus, pg. 80) per turn on its turn. The shadowgarms will attack the PCs on their own initiative. Killing a shadowgarm only makes the creature's corpse disappear as if it was the product of a Summon Monster spell.
After four shadowgarms have been summoned this way, an eldritch howl will emanate from the pool (as the Shadow Mastiff's "Bay" special ability). On the ink pool's next turn, the pool will summon a shadow mastiff (Bonus Bestiary, pg. 16), who will attack the PCs on its initiative. If the shadow mastiff is slain, it's corpse will remain as if the product of a Planar Ally spell. If there are more than four PCs, the ink pool will summon more shadowgarms until the number of shadowgarms summoned equals the number of PCs. Once it has done so, the haunt will destroy itself.
WEAKNESS
This temporary haunt may be damaged by evocation spells with the Light descriptor, cast at the pool of ink as a touch attack (Touch AC 10). Each attack done in this way will do 1d4 damage to the haunt. The duration of the light spell (10 minutes/ level) is ignored in this case. If the haunt's HP is reduced to 0 in this manner, it is considered destroyed.
DESTRUCTION
If the haunt is destroyed, the pool cannot summon any more monsters. The ink pool will disappear, but the creatures it summoned prior to its destruction will still exist and attack as normal. The PC who destroyed the ink pool must make a DC 16 Will save or become frightened for 1d4 rounds, seeing a dark silhouette of Ilnerik trying to grab and choke the PC. If the PC saves, he still sees the silhouette, and becomes shaken for 1 round.
After the haunt is destroyed, the diary is still legible, but the writing appears as if the pages had been soaked in water, causing the letters to become cloudy. PCs may also find their fingers ink-stained after holding the diary for too long, but otherwise the diary acts as a normal book once again.
