Grindiok the Stoneball Mason is a minor entity of the series of the Battle Day/Exchange Student Zero Saga.
He has long grudge against Hiro since his defeat on their battle. Believing he was cheated, he waited until the day Hiro will use the board and get his rematch.
He had a short feud with John, when Hiro refused to battle him and instead the faced off with the new user of the board. None of them won, but surely got to endure the most injuries.
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- His card is from the Roller Clash Expansion.
- His Appearance is based loosely on Proto man from the Mega Man series.