Hoar Frost

A mage strides into a large cavern filled with ores and lit by a lava lake. He constructs a Freezing Rune and activates it. The Frost rapidly spreads outward along the walls encasing the entire room even the ceiling in ice. The lava lake smothered in obsidian as it cracks and cools. The mage pulls out an iron pickaxe and slams it into the ice. The pickaxe shatters into dust. From the impact point, blue lightning cracks race along the ice and embrace the room. In a white flash the room shatter and blocks rain down all around. The mage places a torch and proceeds to pick up his earnings.

Frost Rune Block
 * 1) Spread over the surface with ice.
 * 2) Detect block break, shatter the entire ice structure in one blow, plus the first layer underneath the ice.
 * 3) Conductance step shatter until the pickaxe breaks
 * 4) Drop blocks by WorldXYZ neighbors
 * 5) CA Frost blocks can be linked back to their creator rune (or central event) by using the metadata value as a lookup for active events. For example, there are two active Frost Spread events right now, this is the second, so all blocks it creates are marked with a two. Linking blocks back to the PersistentRune object will allow you to calculate total energy spent and remaining in the rune.

Uses

 * Smooth out a cavern by knocking it out one block everywhere
 * Destroy a structure you don't want anymore
 * Mine by blowing out the walls
 * Create an ice sphere from the ocean for a Faith ship
 * Freeze over a lava lake

Counterplay
A Frost boss that excretes flows of ice that try to encase you. You damage him by breaking ice blocks, which you'll need to do to survive. If he encases you (ice doesn't cause suffocation) then he comes over and rakes you with his claws.

Spilled Qixsilver could have an option of causing a frost plague if not Greek Fire. Greek fire or light could remove ice without breaking the structure. On block break, check to see if the block is ice.

How do you defend against Frost Plague? What's to keep it from being a griefing tool? Torches and light level. Normal Domain protections apply. Pickaxe durability limits total impact (still can be big).