When a nearby unit attacks, the Sharpening Stone has 4 % chances of showing sparks that hit a random monster and inflict zone damage. Damage is equivalent to 200 % damage to the Whetstone.

Each time a unit next to the Sharpening Stone attacks, it causes a spark which inflicts 8 % of its damage to a single target. When units next to the Sharpening Whetstone merge or their merge rank increases, the damage inflicted by the sparks Sharpening Wheels increase from 25 %.

The sparks have 50 % chances of generating spark additional.

The damage inflicted by Sharpening Wheels on multiple targets is no longer reduced, inflicting 100 % damage to single targets.

When a Grinding Wheel is fused or its fusion rank increases, all Grinding Wheels overheatincreasing their damage by 10 % for 10 seconds. With each overheating, the duration of the effect increases by 2 seconds, while the damage bonus increases from 1.5 %.

When 3 Sharpening wheels are side by side, they overheat, increasing the damage they inflict by 30 %.

Whetstone's critical chance increases by 1 % at each merge rank.