Tetris DX

Not to be confused with Tetris Deluxe, a game released for western mobile phones.

Tetris DX was a Game Boy Color game as an enhancement of Nintendo's original Game Boy Tetris, with two added gameplay modes (Ultra, lasting 3 minutes; and Vs. CPU, a match against the computer), a profile/save feature, and color graphics on Game Boy Color and above. In addition, the game's rotation system had a glitch which lets a player move any tetromino except O upward by holding the direction against a wall while rotating in the opposite direction.

Modes

 * Marathon (score maxes at 9,999,999)
 * True 40 lines mode (not 40 "points" like in Tetris Worlds)
 * Vs. CPU opponent

Rotation system
The rotation system is an early version of what would become SRS. Like in SRS, tetrominoes of width 3 rotate as if in a bounding square; unlike in SRS, L, J, and T start flat side up. TDX first tries rotation about the center of the box (the blue circle). If this fails, it tries rotation about an alternate center displaced by one cell (the gray circle). For I, S, and Z, this center starts out one cell above the ordinary center; for L, J, or T, it starts out one cell below. Alternate rotation resets the gravity timer.