Tainted

Tainted creatures:

Aberrations, extraplanar creatures that are not classified as 'Lawful Outsiders' (basically, anything that's extraplanar and isn't an Inevitable, Formian, Modron, or level 20 monk - it does work on devils and angels - get off my plane!), and undead.

"Non-Lawful Outsider Extraplanar creatures" means "things that are extraplanar on Eberron" - if you follow them back to their home plane, they still count.

Explanation by Developer Eladrin: http://forums.ddo.com/showthread.php?p=3255381#post3255381