Hail Trap CR 10
Type mechanical; Perception DC 25; Disable Device DC 30
Trigger location; Reset automatic (for 2d6+1 minutes)
Effects Atk +15 melee (10d6 bludgeoning); multiple targets (all targets not directly under cover); knocked prone (1d6 cold per round; DC 20 Escape Artist, Strength, or CMB check to escape; immunity to falling hail damage; DC 25 Reflex negates); treat area as difficult terrain; flooding after 6 rounds (see below)
Normal weather effects become deadly when the PCs are the size of a copper piece; should they be caught out in the open, the hail trap might do them in if they can’t find shelter! Though become trapped under a piece of ice from the hail trap is unpleasant, it offers some protection and can also be destroyed (hardness 1, 20 hp).
After 6 rounds the area under the effects of the hail trap becomes flooded, requiring DC 15 Swim checks to stay afloat (creatures hit by the hail trap while swimming are not trapped.)
[Submitted by Rory Toma! Tune in on Meta Thursday to read this month' s special rules for extremely small adventurers!]