20G

20G is a term that refers to when the Gravity is set to 20 cells per frame. Since most Guideline-based games have pieces appear on the 21st or 22nd lines of the playfield, they will instantly drop to the bottom in one frame. The term can also broadly refer to any game or mode wherein pieces instantly drop onto the stack as soon as they enter the playfield. Since most modes of many official Tetris games do not set gravity above 15, 20G is typically reserved for games catering to high-level play, or its own separate mode.

Games with 20G modes

Tetris: The Grand Master series

Tetris The Grand Master was the game that coined the term for 20G, and one of the earliest Tetris games to make gameplay changes so such speeds could be playable. In TGM1 and TGM2 (Master mode), 20G speeds begin at level 500. In T.A. Death and TGM3's Shirase, pieces always move at 20G, while in TGM2's Normal and TGM3's Easy, 20G activates at level 300 and 200 respecitvely. The behavior of this mode closely resembles if one were to hold up in TGM2 and 3.

Guideline-compliant games with 20G

• Tetris Kiwamemichi is the earliest non-TGM-related official Tetris game with 20G gravity; however, there is a long post-entry delay, which means that a piece can still freely move horizontally within the spawn area for a half-second before gravity is applied.
• Minna no Soft Series: Tetris Advance has an Advance mode, which is unlocked after completing Challenge mode. In Advance mode, gravity is fixed to 20G.
• Tetris: New Century has "Extra" mode, where the level increases every 4 line clears. Lock delay decreases upon reaching 20G.
• Tetris DS' Standard mode, Tetris Online Japan's Marathon mode, Tetris Friends' Survival mode, Tetris (tetris.com), and Tetris Ultimate's Endless mode have 20G gravity start upon reaching Level 19; if Endless is toggled on or the mode clear line amount is higher than 200, the lock delay either remains constant (Tetris DS) or decreases per level (Tetris Ultimate / tetris.com) after Level 20.
• Tetris Zone, Tetris Party, Tetris: Axis, Tetris Ultimate (3DS version only), and Tetris Effect have a separate "Master" mode, in which the lock delay also decreases per level. The mode ends after clearing 150 lines (Tetris Party / Tetris: Axis), 200 lines (Tetris Zone), or 300 lines (Tetris Ultimate / Tetris Effect).
• Tetris (PlayStation 3) contains "Radical" mode with 20G gravity; the player must clear 40 lines to complete the mode.
• Tetris 99 also contains 20G in Invictus and 999-Line Marathon modes.

Strategies

A piece cannot move across other blocks if the playing field is uneven.

Playing field

T moved right

One structure that will allow a piece to move either left or right is a pyramid:

With ARS, every piece has an orientation achievable during entry delay that will allow it to land on the tip of the pyramid -- column 5. From this point, the piece can be moved either left or right as necessary. Having column 5 higher or on equal level with surrounding columns helps maximize the number of moves that can be performed with a given tetromino. Still, the player should make an effort to avoid overstacking in the center.

T.A. Death mode

T.A. Death is a mode made famous by the "Tetris Japan Finals" video that has been duplicated dozens of times on YouTube, featuring instantly dropping tetrominoes. The difference between death mode and 20G is un-noticeable until later stages in the game in which ARE starts to decrease and lock delay is very low. Arika currently hosts a video showing a GM grade in Death mode here.