Wood Man's stage has two sets of unused palettes. There is coding in the game for enemies to drop E-Tanks upon death, but the code is typically rendered inaccessible due to its potential game-breaking effects. They mean, appropriately enough, 'emptiness'.
These katakana symbols 'aki' were used to fill empty spaces in the enemy graphics. While a similar tile with no shadow is used twice in a single room, this one isn't.
Top-left and bottom-left corners exist as well, which actually were used in a single room. This is probably the most significant and mysterious set of unused tiles in the game. Hidden amongst the background tiles is what appears to be a Met generator, judging by the Met-sized mouth and obviously Met-like features. Only vertical screws use more than five tiles. A tile to be used in the center of horizontal screws with five tiles. Introducing many new concepts and improving on all the flaws of the original, this game is considered by a number of fans to be among the best of the series. Mega Man 2 is, as you may have guessed, the second entry in a very long-running series.
