Grindstone

When a neighboring unit is attacking, there is a 4% chance that Grindstones will give off sparks that hit a random monster and do area damage. The damage is 250% of the Grindstone's damage.

Every time a unit next to a Grindstone attacks, the Grindstone gives off a spark that does 10% of its damage to a single target. When units next to a Grindstone merge or increase their merge rank, the damage done by the Grindstone's sparks increases by 25%.

There is a 50% chance that spawning sparks will generate one more spark.

The damage Grindstones do to multiple targets is no longer reduced, leaving it at 100% of the damage they do to single targets.

When Grindstones merge or increase their merge rank, they overheat to increase their damage by 10% for 10 seconds. With each transition into the overheated state, the effect duration increases by 2 seconds, while the damage bonus increases by 1.5%.

When 3 Grindstones are next to each other, they overheat and increase the damage they do by 30%.

Grindstones' critical chance is increased by 1% for every merge rank.