S.Peelman on 14 December 2014
I see Wright doesn't dare a second guess. Come on, this shouldn't be hard, it's very well known. I'll even add a second hint 
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Game #18
This game's major feature, which also conveniently allowed the game to handle it's system's shortcomings, was proto-typed in another game that appeared earlier on the same system. There, it was used mainly in, but not exclusive to, one particular level.
This main feature resulted in levels made mainly of a particular geometrical shape.
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