Darkstalker

(Lords of Madness, page 179, DnD 3.5)

[General]

You have learned how to stalk and surprise creatures whose senses are very different from those of a humanoid.

Benefit

When you hide, creatures with blindsense, blindsight, scent, or tremorsense must make a Listen check or a Spot check (whichever DC is higher) to notice you, just as sighted creatures would make Spot checks to detect you. You cannot hide in plain sight unless you have that ability as a class feature. In addition, you can fl ank creatures that have the all-around vision special quality.

Normal

Creatures with these senses do not need to make Spot or Listen checks to notice other creatures within range. Creatures with all-around vision can't be flanked.