Blood Grate

Blood grates ref lect the fomorians’ fascination with butchery, even in battle. Not only do these hideous contraptions revitalize the fomorians and their allies as they fight off invaders, they also nourish the fortresses themselves with intruders’ blood.
    A blood grate typically fills an area of 4 to 6 contiguous squares (typically in a square or rectangular layout), though larger grates are rumored to exist in the grandest fortresses of Inbharann.
    A blood grate can be identified with a DC 25 Arcana check.

    Effect: The first time in each encounter that a living creature on a blood grate takes damage, the nearest enemy within 5 squares gains temporary hit points equal to half the damage dealt. The blood grate is then deactivated until the end of the encounter.
    Usage: Most Inbharann fortresses include several blood grates at key defensive positions, which simultaneously nourish the fortress and revitalize its defenders. The fomorians and their servants maneuver enemies atop the grates to gain stamina when those foes are wounded.

Published in Underdark, page(s) 103.