Necroplasm

These foul undead consist of a few bones and an envelope of ectoplasm. They appear as a skull and a pair of skeletal hands wrapped in a vaguely humanoid blob of slime. Its lower half is a column of ectoplasm that leaves a trail as it slithers along. 

Source: D&D Ghostwalk 3.0

     Necroplasms are undead creatures created by Necromancers. These magic users deal in Ectomancy. Ectomancy takes raw ectoplasm(the substance that ghost are made of) to create these creatures. Necroplasms slither about leaving trails of ectoplasm as they travel. If an adventurer encounters this trail within 10 minutes of a Necroplasm passing they can easily track this creature. If more then ten minutes go by the ectoplasm fades away.

     Necroplasms are semi-intelligent undead who hunt in gangs of 2 to 5. They seek out living creatures so they can drain their bodily fluids and create new Necroplasms. They attack victims by attempting to grab them so they can begin draining their fluids. Once engage with a target they don't let go unless destroyed.

Combat: Necroplasms are medium undead. They are Challenge Rating of 3.

Drain Fluids: Once grappling a foe they automatically drain 1d2 points of constitution. The ectoplasm that surrounds their body turns the color of the fluid being drained. For example if they are draining a human they turn a deep red.

Create Spawn: Once a victim has been slain the Necroplasm vomits ectoplasm over their body. After one minute the victim turns into a Necroplasm.

Improved Grab: If a Necroplasm claw attack hits its opponent it automatically attempts to grapple them. As long as they maintain the grapple the victim takes automatic claw damage and fluid drain.

Misc Traits: Fast Healing 2, Turn Resistance +2, Undead traits.

Adventure Seed:

-The group encounters a Ghost who is slowly fading away. His ghostly substance has been diseased and he needs raw ectoplasm to continue his ghostly existence. Unfortunately the ectoplasm lies in a hidden vault guarded by Necroplasms.