Skimming is a clearing method by which a player can use to make a stack even. Skimming is done by placing a tetromino either at the edge or at the surface of a stack and cleaing a line as a result. The technique is favorable in multiplayer tetris because it can save a player from topping out, flatten the field, or allow a player to tetris.
Skimming is especially effective in games that use combo scoring. In other games, skimming forfeits "back-to-back" bonuses and is penalized with more line clear delay per line.
When a player is starved of I tetrominoes, they have to depend on other tetrominoes to keep themself from topping out or to keep their field stable.
A T can be used to skim, either directly or by creating an overhang to a T-Spin Double.
Funnel[]
A field may not be set up for skimming without covering the open column. Stack around the open column to create a funnel for skimming efficiently.
A funnel may be created by filling up the necessary cells to create the indent.
If there is already an indent, fill up the cells to create the wall.
Inverted Funnel[]
Funnels don't have to be limited to long and empty single columns.
Line Clear[]
A line clear can be used to create a funnel.
In this example, using an L to clear the far right column will not result in a funnel. If an I was to be used instead, a JZ funnel will be created.
Tetrominos can create different funnels depending on their orientation when used to clear a line.
Different tetrominoes can create the same funnel depending on their orientation when used to clear a line.
Overhang[]
Funnels can be formed by rotating tetrominoes under overhangs.
Funnels can be set up without utilizing the open column.
Suspended Funnel[]
Funnels can be extended over a column.
Alternate[]
Funnels can be mirrored with various line clears that raise the wall on the opposite side.
The concept can be taken further. In this example, the S tetromino can convert the LS funnel into a JZ funnel. The process may be repeated until the wall on either side of the funnel becomes too short to skim any further.
Inverted funnels can be mirrored efficiently with a J/L or T tetromino.
Fill[]
When unable to tetris because of a funnel, fill it up. The main idea is to fill up more rows than the amount you clear. Technically, the I tetromino would be the best choice since it clears no rows, but it requires the player to have another I tetromino on hand. Therefore, the next best choices are the L, the J, and the T because they clear only one row for every 2 they complete. The S/Z tetromino clears two rows for every two rows it completes, which cancels out any effects.
Flatten[]
Step pyramid and castle structures may become an obstacle when stacking for a tetris. Only specific tetrominos can fit, which limits a player's placement options. Minor line clears can be performed to flatten the structures.
Order[]
When skimming consecutively, the order in which tetrominoes are used can make a difference. Tetromino properties have to be considered.
In this situation, clearing with an S first eliminates the funnel, disallowing any further skimming without covering the open column.
Instead, if an L was to be used first, the funnel would still exist.
The same principle also applies to inverted funnels. In this example, clearing with a T first takes away the opportunity of skimming with an L.
If the L was to be used first, the funnel would still be able to accomodate the T.
