Mushroom Arch

The primal mud (see below) found in various portions of the Feydark gives rise to several secondary terrain features of interest, including the mushroom arch. Also called an arch of wonder, a mushroom arch appears as a series of glowing mushrooms (frequently pale purple) that grow together to form an arch over a corridor through which a creature can pass.
    A mushroom arch can form over a tunnel of any size up to 4 squares in width or height. It can be identified with a DC 20 Arcana or Dungeoneering check.

    Effect: A mushroom arch gives off dim light in a 5-square radius. It also can affect creatures that pass through it, but rarely the same way twice. The effect is sometimes negligible, other times positive, and occasionally awful.
    A creature that walks through a mushroom arch (or moves to stand directly beneath it) is affected automatically; roll a d10 and refer to the table below to determine the effect. A fey creature that walks through a mushroom arch adds 2 to the roll. Any time a creature triggers a mushroom arch, the power resident within it is temporarily drained, and the arch can’t be activated again for 1 hour.

1-2Ongoing 5 damage per tier (save ends)
3-4Slowed (save ends)
5-6No effect
7-8Bioluminescent haze grants concealment until the end of the encounter
9 or higherRegeneration 2 per tier until the end of the encounter

    Usage: Place a mushroom arch over a tunnel leading directly to a combat encounter to start the encounter off with a variable effect. Alternatively, placing the arch within an encounter space—perhaps in a tunnel connecting two areas of the battlefield—allows it to change the tenor of the fight in mid-combat.

Published in Underdark, page(s) 101.