Minna no Tetris is a licensed Plug & Play Tetris game which notably comes with a Tetrimino-shaped controller.
Debug Play#
Boot the game while holding A + B + Up + Start, and the game will redirect to some sort of debug gameplay mode, in which there is generally no restriction on piece placement. The D-Pad moves the pieces, while L and R, which are normally used for holding them, places them on the current position instead. Note that placing a piece above the playfield will cause an instant game over.
(Source: tikal.)
Diagnostic Leftovers?#
Found from 0x175280 in the game's ROM are graphics for the Diagnostic Mode seen in many Plug & Play units developed by V-Tac, though it doesn't seem that it can be accessed here.
(Source: David Haywood)