The door to this room is closed, but it is neither locked nor jammed. If the players do not have combat directly before this room then roll listen/move silently checks against the grimlock. If they have a battle or create some other ruckus (as adventurers often do), then the grimlock is already prepared.
Description if the check succeeds
You open the door to a large room that has been roughly hacked out of the earth. Bones and decaying equipment litter the floor with some coins glinting in the light. Off to the side of the room is a small cot with a grayish humanoid laying on it. Its head turns to face you and it would be staring if it had any eyes to stare with. It hisses and throws a glass vial filled with inky blackness at you.
The grimlock will make his way to the back of the room slowly, firing bolts at the party as they stumble out of the darkness.
Description if the check fails
You open the door to a large room that has been roughly hacked out of the earth. Bones and decaying equipment litter the floor with some coins glinting in the light. You see a overturned cot on one side of the room.

At the back of the room is a small nook that the grimlock is hiding in. As the party makes it to the middle of the room he throws a Darkblot potion at the party. He will then circle the room to confuse the party about his location.
Grimlock
HD 2d8+2 (11 hp)
Initiative +1
Speed 30 ft
AC 15 (Touch 11, Flatfooted 14)
Battleaxe + 4 ( 1d8+3 / x3)
Crossbow +2 (1d8 / 19 - 20 x2)
Fort +1, Ref +4, Will +2
Terrain notes
The rough spots in the room count as rough terrain. It takes two squares of movement to move one square through this terrain. If a creature that cannot see moves through it, that creature must make a DC 10 balance check while moving through the square for each square or fall prone.
Darkblot Potion
A Darkblot potion is a black colored potion that is made by mixing Inkroot, Powdered Onyx and a Pseudodragon Claw. Inkroot can be found glowing in shadowy area deep in the forest. Powdered Onyx is often seen in the apothecary chests of Witch Doctors, and a Pseudodragon Claw can be found on, well, a Pseudodragon. These must be ground together, along with 33 gold pieces worth of common material. It takes a DC25 Craft (Alchemy) Check to create a Darkblot potion.
This potion mimics the darkness spell. It shatters on impact, creating a 15 ft radius circle of darkness as listed in the the players handbook that lasts 10 rounds. If it is thrown at a creature, that creature is partially coated with Darkblot, gaining a +5 bonus on all hide checks for 10 minutes. It can also be poured onto a creature to give this bonus without creating an area of darkness. Treat it as a splash item when thrown. Its market price is 100 gold pieces per vial.
Aftermath and Loot
The grimlock has few possessions besides those left by adventurers that it has neglected to move. 50 silver pieces, 60 gold pieces and 2 Darkblot vials are scattered about the room. With a DC 20 search check the party also finds a gem worth 20 gold pieces.
