Monster: Void Stalker
Overview
Void Stalkers are spies and assassins for the Elemental Lords. When a being angers the rulers of the elemental kind, but is too powerful or too evasive to simply destroy, they send out a Void Stalker instead.
Made of pure nothingness, the Void Stalker can travel freely between dimensions and planes in pursuit of its given target. Due to their nature, physical barriers of any material or make are completely useless against Void Stalkers, as they simply pass through the gaps of void between the materials. Magical defenses and fields do better, but Void Stalkers can negate and destroy most of those as well, save for ones created by the most powerful of mages, demigods or divine beings.
Stats and Abilities
AC: 0 [19], HD: 10, To Hit: +10, Attacks: 2x silver needle (3d6 damage), Movement: 120', Saving Throws: As Greater Elemental, Morale: 12, Alignment: Neutral, Numbers Appearing: 1, Treasure: 2x silver needles
Abilities and Behavior: As stated above a Void Stalker can freely travel between planes, demi-planes and dimensions, and is very resistant to being banished (as it was never summoned in the first place), though not immune to it. It can pass any material barrier without it impeding its movement in any way.
A Void Stalker can destroy lesser magical barriers with relative ease, though it might struggle with particularly strong or potent ones. However it is also a very patient hunter (as an elemental, time means little to it) and will wait for an opening for thousands of years if necessary.
Void Stalkers are immune to all forms of elemental damage, and can only be physically harmed by magical weapons of +3 or greater. They are also immune to all negative energy attacks, being made of it themselves.
Once a Void Stalker has a shot of its stated target it will attack, attempting to stab its target with a silver needle (it carries an additional one for backup). Any successful attack with a silver needle shatters it instantly, lodging a splinter of the needle into the soul of the target. Should a target survive the attack, the sliver of the needle forever signals them as marked for death by the Elemental Lords.
Any Outsider being can instantly recognize the mark in someone, no matter their physical form (or lack of it) and many would do anything they can to deliver the bounty to the Elemental Lords, as the rewards and gifts they offer in exchange are wondrous and great.
Not even death dislodges the shard, as it travels with the disembodied soul and will remain stuck in it until removed by a power of a being equal to or greater than the Elemental Lords themselves. Most such beings dare not risk the consequences of removing the bounty.