Tetris (NES)

Tetris (Russian: Те́трис, pronounced [ˈtɛtrʲɪs]) is a Russian tile-matching puzzle game, originally designed and programmed by Alexey Pajitnov. Although two versions of Tetris were published in the United States, Nintendo's version was the only version that was properly licensed for distribution. This version sold 8 million copies worldwide. Nintendo's NES version lacked the side-by-side 2-player option featured in Tengen's version.

Atari Games, legally owning the rights to manufacture an arcade version of Tetris, later ported the game to the NES and released an unlicensed NES version in 1989 under its Tengen brand. However, there were issues with the title's publishing rights. After much legal wrangling, Nintendo itself ended up with the rights to publish console versions of Tetris, leaving Atari with only the rights to arcade versions. As a result, the Tengen game was only on the shelf for four weeks before Atari was legally required to recall the game and destroy any remaining inventory of its NES version.

Game modes

 * A-Type: Endless, choice of starting level (0 through 9), clear 10 lines to advance to the next level.
 * B-Type: Clear 25 lines, choice of starting level (0 through 9), and choice of starting garbage height (0 through 5 where each number is 3 more lines of garbage).

Other options

 * Music: Three choices of music can be selected before each game, simply called "Music - 1," "Music - 2," and "Music - 3."
 * Toggle Next piece: To hide or show the display of the Next piece, press.
 * Harder levels: To start a game from levels 10 through 19, highlight a level from 0 through 9, press and hold, and press to begin a game at a level ten higher than the one you highlighted.

Lack of 2 Player mode
This version of Tetris does not present a 2 player mode to players. However, the ROM does contain support for a 2 player competitive mode. By setting RAM address $BE to 02 (or using Game Genie code VUXEILXX) one can activate this unfinished mode. While the basic rules are in place and the game is "playable", there are numerous issues: However, a resourceful hacker by the name of infidelity has hacked the ROM to provide complete support for, and access to, a 2 player mode along with a few other improvements. The name of this hack is "Tetris Zero" and it can be found here.
 * Standard 1P mode screen layout is always used (no 2P mode layout exists in the ROM).
 * Next piece displayed in wrong location.
 * Colors are glitchy.
 * Music alternates between fast and slow when one player nears the top of the playfield.
 * Crashes to copyright screen when game is over.
 * Garbage attacks are fully implemented.
 * A-Type setup/high score screen is missing a large chunk of tiles.
 * Both game types have empty high score tables.

Technical details
The rotation system is a right-handed Nintendo Rotation System. Lock delay, wall kick, and hard drop are not present.

Despite the title's popularity, its Delayed Auto-Shift (DAS) mechanics were not well-understood until player Kitaru analyzed its internal memory values. The game keeps a hidden count of how many frames the left or right button has been held down for. This is called the "DAS counter." After holding down left or right for 16 frames, the piece moves left or right by one column, and the DAS counter resets. Only, it doesn't actually reset all the way back to 0. It instead resets it to 10. After 6 more frames, it will reach 16, the piece will move another column, and the counter will reset back to 10. After the left or right button is released, and left or right is pressed again, the counter will reset all the way back to zero. In effect, pressing and holding down the left button will first move the piece 1 column, then after 16 frames it moves another column, then it will move a column every 6 frames.

There are a few other very interesting details. During the Entry Delay (aka ARE), the DAS counter effectively freezes. A player can release and tap left or right, and after ARE is over, the counter's value will not change. The only thing that resets the counter to zero is by pressing down the left or right buttons, and doing so in a time other than ARE. Simply releasing the thr direction button will keep the counter "charged." A good strategy, then, is to charge the DAS through normal play and then carefully switch directions only during ARE. This way, the pieces will continue to move quickly without needing to recharge the DAS.

Another interesting feature is what happens when dead tetrominos or a wall blocks the active piece. The DAS counter instantly jumps to 16. A player can strategically use this feature to quickly charge the DAS counter for next-coming pieces.

Soft drop speed is 1/2G. ARE is 10~18 frames depending on the height at which the piece locked; pieces that lock in the bottom two rows are followed by 10 frames of entry delay, and each group of 4 rows above that has an entry delay 2 frames longer than the last. line clear delay is an additional 17~20 frames depending on the frame that the piece locks; the animation has 5 steps that advance when the global frame counter modulo 4 equals 0. As a consequence, the first step of the line clear animation is not always a set number of frames. DAS charging is completely dead during ARE and line clear. While tapping or changing direction during active time would reset the counter, inputting left or right during ARE or the line clear animation has no effect on the value of the counter. This means that any DAS charge left over from the previous piece can be redirected during ARE.

PAL release
The PAL NES is specified to run at 50.0070 frames per second. Rather than play as a slower version of the NTSC original, the game was rebalanced with a modified set of frame timings for its PAL release.

DAS initial delay is 12 frames, and then every 4 frames through subtraction from the DAS counter. The behavior of ARE and line clear appear to be unchanged. The modified gravity table attempts to follow the same progression, but lack of resolution causes some significant changes in the speed of later levels; given that Levels 08 onward are each 1 frame faster than the original NTSC speedcurve, the game reaches speeds of 1G at Level 19 rather than Level 29.

Although the improved DAS facilitates play at 1G speeds without rapid tapping to some extent, prolonged survival remains dubious; play is still restricted to the bottom rows of the playfield, and the high gravity coupled with a faster (and therefore harder to "skillstop") DAS make it incredibly difficult to maintain a clean stack. It is most likely infeasible for a human player under regular conditions to attain a max-out score in the PAL version of NES Tetris.