Look out Below!
House rules for falling creatures.
A flying creature that is knocked prone falls (RC p210). There are two distinct types of falls depending on whether the fall is controlled or uncontrolled.
An example of a controlled fall is when the creature is conscious and has a fly speed or some other power that allows a controlled descent. In this scenario, the rules on p209 of the Rules Compendium state that the creature can safely fall a number of squares up to their fly speed without taking damage. If the creature can fall without taking damage according to these rules (or any other effect such as feather falling), this leads to the following scenarios depending on what is below the flying creature.
Non-Hindering Terrain: If the creature is falling above regular (non-hindering) terrain, the creature falls as per the rules on p209 of the Rules Compendium.
Hindering Terrain: If the creature is falling above any hindering terrain (e.g. a pit of lava, a known trap, etc.) then the creature is allowed to make a saving throw similar to the throw for forced movement (see RC pp212-213). On a successful save, the creature can glide the minimum number of squares needed to avoid landing in the hindering terrain (up to the creature’s fly speed) and then proceed with the rules on p209 of the Rules Compendium. If the creature fails their save, or if, after gliding their fly speed, they are still above the hindering terrain, they fall into the hindering terrain according to the rules on p209 of the Rules Compendium and any effects of the hindering terrain take effect.
There is one exception to this rule:
If the hindering terrain is simply a deep hole or other precipice without any hindering terrain at the bottom, then the rules on p209 of the Rules Compendium apply.
Creature(s): If the falling creature is above another creature or creatures when it falls, all of the creatures will be squeezing at the end of the fall. Each ground based creature can make an opportunity attack against the falling creature with a -5 to the attack roll as the creature enters their space (RC pp249-250).
An uncontrolled fall occurs when the creature’s fall causes it to take falling damage. The following scenarios occur during an uncontrolled fall depending on what is below the falling creature.
Hindering or Non-Hindering Terrain: If the creature is falling above regular (non-hindering) terrain, or hindering terrain, the creature falls as per the rules on p209 of the Rules Compendium.
Creature(s): If the falling creature is above another creature when it falls, the creature(s) on the ground suffer collision damage. The creature(s) on the ground take half of the damage that the falling creature takes from the fall. At the end of the fall, all of the involved creatures are prone and squeezing.