The following is a list of features that a version of Tetris may or may not contain. Whatever version of Tetris you are playing is likely to have some of these. Older version will have fewer of these features, and newer versions will have more of them.
Delayed Auto Shift (DAS) refers to the behavior of most falling block puzzle games when the player holds the left or right key. The game will shift the falling piece sideways, wait, and then shift it repeatedly if the player continues to hold the key. See Controls for more information.
Lock delay refers to how many frames a Tetromino waits while on the ground before locking. Classic games lock Tetrominos immediately once it has fallen to the ground, while some newer games give the Tetromino some time before locking.
Some games such as the Puyo series use a fixed amount of lock delay for each piece, pausing the timer while the piece falls, resetting it only when a new piece enters (entry reset). Some games, especially those using Sega rotation or its successors, reset the timer every time the piece "steps" downward (step reset). Games following the Tetris Guideline generally reset the timer on any successful shifting or rotation (Infinity or move reset).
Entry delay, commonly known as ARE among players of Japanese Tetris games, is the period of time between the lockdown of one Tetromino and the appearance of the next Tetromino. This delay is a feature often seen in Japanese games, most of them influenced by Sega's early 1988 arcade version. Depending on the level, the amount of delay may shorten. Generally, during the delay, the player must wait for the next Tetromino to appear, and cannot actively cause anything to happen.
The delay is a vital gameplay factor in TGM. It does not exist, however, in popular American and European versions such as Tetrinet and most Tetris Guideline-compliant games, except possibly after a line clear. Some games that have entry delay or line clear delays allow the player to "charge" DAS by holding the movement key during these delays, so that the piece starts moving sideways as soon as it appears.
Initial rotation and Initial hold are features that make the game accept rotation/hold button inputs while the next piece is still in the preview area. With initial rotation, when the player holds down the rotation button after the previous piece has locked down but before the next piece comes into the well, the next piece will come into the well in an already rotated state. Initial hold works similarly, as the piece will be already swapped with the hold piece when it enters the well. Initial rotation and Initial hold first appeared in the Tetris: The Grand Master series. Without entry delay, these features can't be implemented consistently, so most Guideline games, which contain no entry delay, do not have initial rotation or hold.
Nearly all falling block games are capable of showing a preview of the next piece to enter the playfield. The next pieces are displayed in a window of the tetrion, generally positioned to the right of or above the playfield. Some of the older games gave more points if the player chose to turn preview off. Many Tetris games released since 1999, especially those adhering to some version of the Tetris Guideline, show three or more next pieces.
The Ghost piece, also called shadow, is a representation of where the current piece will land if allowed to drop into the playfield. It is generally colored fainter than the falling piece and the blocks in the playfield. As the player moves the falling piece, the ghost piece moves below it; when the piece falls far enough that it overlaps the ghost piece, the falling piece is always drawn in front.
Older games did not have a ghost piece, but all games that conform to the Tetris Guideline allow the player to use a ghost piece at all times. The ghost piece reduces the number of misdrops, especially for beginners or for high-speed players who use hard drop, but some players who are migrating from games without a ghost piece have trouble adjusting to the ghost piece when they fail to distinguish it from blocks in the playfield.
Hold piece is a feature of most newer Tetris games starting with The New Tetris. The top left of the tetrion has a window called the hold space that displays a Tetromino. At any time starting when a Tetromino enters the playfield until it locks, the player can press the Hold button on the controller to move the active Tetromino into the hold space and move the Tetromino that was in the hold space to the top of the playfield. A Tetromino moved into the hold space is unavailable for switching out until the Tetromino that was moved out of the hold space locks.
Hold piece was introduced as part of the development of Square Tetris mode (introduced in The New Tetris; also appears in Tetris Worlds), making it easier for the player to assemble squares. Its inclusion in standard Tetris is controversial, as some critics have claimed that it makes the game too easy.