Permanent life draining zombies.

[Rustweaver]

Yes they are the yellow zombies ("black death").
The monsters can be found in Normal, Nightmare, and Hell difficulties.
They appear on levels 3, 4, 5. They are the only monster that reduce your HP permenantly.
This info can be found here: http://www.lurkerlounge.com/content/view/751/110/

Thanks for the info and link.