Necrotic Ground

This area is infused with necrotic energy. All light sources appear slightly dimmer, and the air is cold and still. Creatures that enter this area feel tired and drained.

    Effect: A creature that spends a healing surge in an area of necrotic ground recovers only half the normal number of hit points. (All other effects, such as additional hit points regained or the bonus to defense from using second wind, are unaffected.)
    Usage: Unless an encounter area consists entirely of necrotic ground, characters will wisely do anything they can to avoid being in the area when they spend healing surges. If you combine necrotic ground with a strong defensive position or another advantageous location, you might force characters into the difficult choice of staying in their good position but gaining less benefit from healing effects, or abandoning their position so that they can regain as many hit points as possible.

Published in Dungeon Master's Guide 2, page(s) 61.