Options

Colors

Classic: (default) Colors identical to those used in NES Tetris. This includes all of the glitched colors that appear starting at level 138, and the wraparound that occurs every 256 levels.
Unglitched: Identical to classic, but without the glitched colors or wraparound. The colors consistently repeat every 10 levels.

Garbage piling

This option only affects multiplayer modes (local and online). If on (default), clearing lines on your board will send garbage lines to your opponent's board. 1 line of garbage is sent for a double, 2 lines for a triple, and 4 lines for a Tetris. Additionally, getting a perfect clear sends 10 lines of garbage to your opponent. When this option is set to off, no garbage is sent.

Hard drop

When this option isn't set to off, pressing the up button will hard drop the active tetromino, i.e. instantly snap it to the bottom of the board.

Off: (default) Hard dropping is disabled. This is consistent with NES Tetris, which doesn't have a hard drop feature.
Without lock: Pressing the up button will snap the tetromino to the bottom of the board, but the tetromino won't be locked until the up button is released. While the up button is held, the tetromino can be moved or rotated. This allows tucks and spins to be performed.
With lock: Pressing the up button will snap the tetromino to the bottom of the board and immediately lock it.

Input delay

When this option is set to on (default), the input delay of NES Tetris (two frames) is emulated. Otherwise, if off, inputs are processed as soon as they are available. The options screen never has input delay, regardless of this setting.

Input handler

The primary purpose of this option is to give mods a way to capture and modify/replace user input, if they wish to provide an alternative input mechanism. For instance, the "tas" mod registers an input handler which sends pre-recorded input from a .fm3 file. Inputs read from a replay file don't go through the input handler and thus aren't modified.

Vanilla: (default) No modifications are made to the received inputs, except that when both left and right or both up and down are pressed, neither input is sent. This makes the game behave more sensibly when controlling with the keyboard, and shouldn't have any effect on a controller since it's not possible to press opposing directional buttons at the same time.
Multidirectional: No modifications are made to the received inputs. Pressing opposing directional buttons at the same time sends both inputs.

Lines per level

Vanilla: (default) The level is incremented following the same rules (and bugs) as NES Tetris: every 10 lines, except that the starting level may last for fewer lines and very high levels last for 800 lines.
Fix high: Identical as vanilla, but very high levels won't last for 800 lines.
Fix all: The level is always incremented every 10 lines, except for the starting level, which still lasts for level * 10 lines.
Constant: The level is always incremented every 10 lines, even the starting level. Useful for practicing transition.

Music

The music played in-game.

Pause

Vanilla: (default) Pausing causes the screen to become all-black with "PAUSE" written in the center, not showing the board until the game is unpaused.
Disabled: Pausing is disabled completely. Pressing start in-game won't have any effect.
Show board: Pausing is enabled, but the board continues to be visible even as the same is paused.

RNG

Classic: (default) Pieces are chosen by the same RNG algorithm used by NES Tetris. The piece is chosen randomly (with some bias), and if the chosen piece is the same as the previous piece, a new piece is chosen (also with bias) and used.
Droughthack: A modification of classic which also re-chooses a new piece if an "I" piece is chosen first. This makes "I" pieces much rarer.

Save highscores

When this option is set to on (default), highscores are saved to disk. Otherwise, if off, highscores aren't saved.

SFX

NTSC: (default) NTSC sound effects from NES Tetris are used.
PAL: PAL sound effects from NES Tetris are used. (TODO: unimplemented)
Off: Sounds effects are disabled.

Speed

This option controls the speed of the game logic. The default value 1/1 instructs the game to run at 60Hz; all other values are fractions to be multiplied by 60Hz to get the new game speed.