Whirlwinds form in areas infused with elemental energy (often in water or air). A whirlwind’s current drags creatures along its path.
Effect: When a creature enters a whirlwind square or starts its turn in one, it moves a distance and direction according to the whirlwind’s strength and direction (as determined by the Dungeon Master). This movement is a slide effect, with the distance and direction determined by the whirlwind.
A creature that wants to fight against the whirlwind can spend squares of movement to reduce the distance the wind slides it (if the creature still has movement left during its turn). The creature can reduce the distance partially, or decrease it to 0, provided the creature has enough movement to do so.
If a whirlwind slides a creature through another square that has a whirlwind, the creature ignores that other whirlwind.
A whirlwind can also move creatures upward. A creature that ends its turn outside of a whirlwind square and aloft falls to the ground if it isn’t flying.
Usage: Whirlwinds increase the amount of forced movement occurring in an encounter, creating a chaotic and moving battlefield that can present difficulties for defenders who like to lock down their opponents. Pair whirlwinds that launch creatures into the air with flying skirmisher that aren’t harmed by the forced movement to increase their movement capabilities. Whirlwinds can also make an encounter in a high location with long falls more dramatic, especially if the characters are fighting opponents with forced movement powers.
Published in Dungeon Master's Guide, page(s) 69.