Choke frost is found in the deepest caves of frozen lands or in the lairs of creatures of elemental ice. This light, white mist congeals into thick ice when creatures or other sources of heat move through it.
Effect: When a creature enters a square of choke frost, it takes a -1 penalty to speed. This penalty is cumulative and lasts until the creature uses a move action to negate it. Creatures that have resistance or immunity to cold, or that have the cold keyword are immune to this effect.
Usage: Use choke frost to slow down characters with high speed, limiting their ability to reach leaders, controllers, and artillery creatures in the back ranks. This terrain also works well with skirmishers that are resistant or immune to cold, allowing them to attack and retreat through choke frost squares, while the characters are forced to move around the terrain or pay the cost.
Published in Dungeon Master's Guide, page(s) 67.