Primal Mud

Life force rises up through the Feydark into the Feywild in the form of primal mud. This organic sludge takes on various colorations, from a brown muddy hue to a clear, viscous slime. It gathers in pools and depressions, from where it is sucked through the Feydark’s root structures up into the Feywild above. Primal mud nourishes the Feydark’s dense subterranean f lora. Brief contact with primal mud heals; lengthier exposure tears down living tissue, returning it to its raw nutrient origins.
    A patch of primal mud typically covers 1 to 3 contiguous squares of cavern f loor, but multiple mud patches are often present in the same large chamber. Primal mud can be identified with a DC 20 Dungeoneering check.

    Effect: Primal mud is difficult terrain. A creature standing in primal mud can spend a healing surge as a minor action. This act temporarily expends the mud’s magic and dries it out, changing that entire patch of primal mud into normal terrain until the end of the encounter. A fey creature that uses this benefit gains 1d6 additional hit points per tier and gains a +2 bonus to speed until the end of its next turn.
    Usage: Use primal mud in particularly long or tough encounters to give the characters an edge in the fight. Alternatively, a wily fey opponent can use primal mud to heal itself and then flee the battlefield, possibly to set up an ambush in a later chamber.

Published in Underdark, page(s) 101.