Puyo Puyo Tetris movement intricacies

Inter-frame processing order
Here are a few tests conducted to reverse-engineer the order in which inputs are handled:
 * Left + right simultaneously - piece shifts right
 * Left + harddrop - piece hard drops, no shift
 * Rotate + harddrop - piece rotates then hard drops
 * Hold left while right DAS charged - piece shifts left, piece stops DASing right.
 * Hold right while left DAS charged - piece shifts right, piece stops DASing left.

Using this test data, we can assume that input is processed in this order:
 * Rotation
 * Hard drop
 * Shifting
 * ? Where DAS/Auto-shifting occurs is unknown at this point

Entry Delay / ARE

 * DAS can be charged during Entry Delay
 * Hard drop inputs during Entry Delay are ignored
 * Tapping Left/Right inputs during Entry Delay are ignored (however, the keyheld event is processed - DAS can be charged)
 * Hold inputs during Entry Delay ignored
 * Rotation inputs during Entry Delay are ignored

DAS Double-Charging
DAS is charged on two separate counters. It is possible to charge both DAS counters at once.

E.g.
 * DAS first piece to right wall. Drop
 * Hold left, do not release right.
 * Das second piece to left wall. Drop. (Left and Right DAS are both charged)
 * Release left key. Piece will go right with DAS Charged.

Input muxing
Puyo Puyo Tetris offers a variety of presets for control configuration. In most presets, some actions have some form of alternate button or input (e.g., the default preset allows pieces to be moved by either the d-pad or analog stick).

The game engine handles this many-to-one relationship between inputs and actions with what one could consider just one "virtual input" per action. If an input for an action is already held, pressing the alternate input will not trigger that action again. (e.g., simultaneously pressing two movement/rotation buttons will not trigger a double tap shift or 180 rotation). Moreover, if both inputs for an action are held, releasing one of them will not do anything special; the game considers the action to have been continuously held. (reference: Kitaru) This means that from an input perspective, no new quirks are possible compared to having only physical key per logical input.