TGM Rotation

TGM rotation is a game play mechanic used in Tetris The Grand Master and other Arika tetromino games, derived from Sega rotation. It is often refered to as ARS (Arika Rotation System), even though some people believe that this name is misleading.

Games using TGM rotation generally use IRS, fast DAS, lock delay, and firm drop, and tetrominoes start out with the topmost block on the top row (generally row 20). The "ARS" and "ARS2" modes of Tetris The Grand Master Ace use a hybrid of TGM rules and Guideline rules.

Basic rotation
TGM's basic rotations inherits most of its properties from Sega rotation, which was used in most previous Japanese arcade Tetris games. Some defining characteristics include:
 * Having 2 (as opposed to 4) rotation states for S, Z, and I tetrominoes.
 * Keeping tetrominoes at an even level while rotating to always allow rotation when the tetromino is on a flat surface (except for the I tetromino - see exceptions below).
 * Pointing the initial stance of the T, L, and J tetrominoes downward.

Wall kicks
TGM pioneered the use of wall kicks, with simple but effective kick rules. These rules were unchanged until TGM3, remaining constant across TGM, TA, TAP, and Sakura Tetris. Up to 3 locations are tried, in this order, before rotation will fail:


 * Basic rotation
 * 1 space right of basic rotation
 * 1 space left of basic rotation

In addition to these rules, there are some extra exceptions where certain wall kicks are not allowed:


 * The I tetromino will never kick.
 * L, J, and T tetrominoes, from their 3-wide orientations, will not kick off their center column. In the situations illustrated below if the [[Image:XTet.png|X]] marked block is occupied.

However, there are very similar situations where additional off-center blocks will enable a wallkick. In the situations illustrated below, the upper blocks are off-center and enable the kick even in the presence of  blocks in the center column.

Clockwise rotation will successfully kick:

Counter-clockwise rotation will successfully kick:

I tetromino's wall kicks
In TGM3, the I tetromino can kick walls. There are 3 different types of wall kicks.

I tetromino's floor kicks
The I tetromino can kick the floor.

Notes:
 * Like hold piece, floor kick can be performed only once per tetromino.
 * The tetromino cannot kick the floor in mid-air.

There are 2 different types of floor kicks.

T tetromino's floor kicks
The T tetromino can escape from a hollow.

Notes:
 * This action can be performed only TWICE per tetromino. See below.

Rotating a T or I tetromino after it has floorkicked will permanently set the lock delay for that tetromino to zero. This is actually what prevents the second I floorkick. After the second rotation is processed, movement gets processed, allowing a shift of one cell left or right if it's done fast enough. Gravity is then applied. If the I tetromino is not in contact with an occupied cell below after processing gravity, any attempt to floorkick will fail, as explained above. If contact does exist, the tetromino will instantly lock down, preventing rotation from being processed at all.

The T tetromino has no such restriction, so it IS possible to make it floorkick twice, but it will lock after the second one because there is no way to process rotation again before it locks.

Right side bias
In TGM's rotation system, the Tetrominoes rotate on only one axis resulting in asymmetrical rotations. In this example, the I piece can't rotate on the left side of the stack;

..Z....... ..Z....... ..XGGGGGGG ..XGGGGGGG .GGGGGGGGG

A situation which would work on the right side.

Notice the I has 1 rotation axis;

ZZCZ I piece's rotation axis

This case does not apply to the T tetromino, as it rotates on its center;

.I. ICI T rotation axis

Mihara's conspiracy
Due to the right side bias with wall kicks, doing this move with a J when there is an empty hole right of the block that the J is caught on will lead to a hole.

L works: J does not... ...unless there is another block to force a kick to the left.

It can however be used to the player's advantage by it being used to jump over spikes.

ACE-ARS and ARS2
Ace's rotation is a hybrid of SRS and ARS. Ace features guideline colors and lock delay is now directly reset by rotation/movement. A maximum of 128 lock delay resets are permitted per piece. Piece spawns that would previously have resulted in death (blocks occupying row 19/20 spawn locations) will now instead cause the piece to spawn higher, to a maximum of rows 21/22. This effectively makes the usable well size 2 rows higher.

ARS2 is available through an Xbox live patch for ACE. Normal ARS features Sonic Lock (locking hard drop) and non-locking soft drop. ARS2 had Firm Drop (instant soft drop) and hard drop (not instant).