How do I use the Rainbow Sword?
I recently collected and assembled the three pieces of the Rainbow Sword. I equipped the item and started a level, but the Rainbow Sword icon was blacked out when I tried to use it.
The Rainbow Sword description says it fires a rainbow blast when powered, but doesn't explain how to power it. How do I use the Rainbow Sword?
The Rainbow Sword is powered by ending your turn on a grindstone. That power is stored until you fire a rainbow blast.
A rainbow blast can be fired in one of 8 directions. A vertical or horizontal blast covers 3 lanes, while a diagonal blast covers an alternating 2/1/2 pattern. It deals 3 damage per enemy and is not stopped by creeps, walls, or any obstacles.
Note that landing on another grindstone while the Rainbow Sword is already powered up does not let you store multiple rainbow blasts at once.