Downstacking

Please note that this article does not take into account details such as line clear delay and attacking power. Those details matter when deciding whether or not you should try to "group" line clears together while downstacking.

Downstacking refers to when you clear down through garbage rows. Downstacking is a challenging skill to master and rich with depth. Inefficient downstacking is often the Achilles' heel of newer players. 

The primary goal is to lower your surface height. Doing so prevents you from topping out. Use as few pieces per garbage row as possible.

Covering Holes


The location of each hole tells you how to place pieces above them. The higher the hole, the more important it is to stack with it in mind. Simply put, try not to stack over holes. You must clear any upstack left above the hole before you can clear the hole itself. The extra upstack requires more pieces to clear.



In this example, stacking over the bottom hole costs at least two pieces more than necessary.

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Every cell of upstack aligned directly above a hole represents an extra line of upstack that later needs clearing. In the example below, the I-piece is the least desirable solution. It leaves behind three cells of residue directly over the 10th column's hole. Those three rows of upstack will cost you roughly eight extra pieces. The S- and J-pieces are much more appealing. They only leave one cell of residue over the 10th column's hole.



Placing the O-piece against the left wall makes it easier to resolve the upcoming holes on the right side.



In this case, the S- and L-pieces leave residue directly over the next hole.





The J-piece leaves nothing over the next hole, but it does leave residue over the hole after that.



The T- and I-pieces don't leave residue over any holes. But the T-piece is best because it clears two lines. It also results in either an I- or J-piece dependency. The I-piece results in an I-piece-only-dependency.



Examples of avoiding covering holes

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Below, it is better to postpone the immediate line clear.

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Managing Upstack Residue


Each garbage row contains one empty cell. Each piece contains four filled cells. Therefore, it takes 1/4th of a piece to clear one row of garbage. This leaves three cells of "residue." Clearing two garbage rows with one piece leaves two cells of residue. Three rows leaves one, and four in a row leaves nothing.

It is possible to clear this residue without using any extra pieces. Below, an L-piece sits directly over the bottom-most hole. Yet this does not cost extra pieces. Its residue disappears as a natural consequence of clearing the holes above it.



As such, spread residue evenly over the surface. This creates more opportunities to clear residue away "for free." Maybe you can place pieces so that they don't cover holes, but it results in awkward surfaces instead. The strategy changes depending on how much upstack covers a hole. When there is a lot, then creating instabilities may not pay off. Much of the time, chances are that you can clear off the upstack naturally before reaching the hole.

When dealing with a hole near the top, it is more worthwhile to forego stability. Learn when to play it safe and when to take chances. You must judge which path best suits the end goal of minimizing overall pieces used per garbage lines cleared.

The first example results in a stabler surface. However, it is more valuable in this case to start clearing garbage while maintaining a "good enough" surface.

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Here, a temporary gap in the surface is likely worth clearing down that garbage.





Finding opportunities to clear lines

Singles and Doubles tend to more efficiently clear upstack than do Triples and Tetrises. Look out for ways of clearing lines with whatever pieces you have at your disposal.


















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Focusing on clearing garbage rows is usually more efficient than dealing with existing upstack rows. Each row of upstack requires 2.5 pieces, but each row of downstack only requires 1/4th of a piece.

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In the below example, both cases leave the same number of filled cells. Both cases clear a line. However, the second case reveals access to the next hole.

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The jagged corner

This shape was shown in the upstack section, but it poses even more danger when downstacking. The Z-piece doesn't resolve it.



Even the J-piece is better, since it will not require more pieces stacked on top.



Maintaining downstack options

Direct upstack residue away from upcoming holes. This creates more choices to clear the remaining hole.

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Keep the area around and above upcoming holes as clear as possible.

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Finding alternatives

It can be risky to hold out for the "perfect" piece. You have to find a spot for every piece before finally getting the right one. This causes unnecessary upstack. Look for alternative methods.






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Platform Stacking

Vertical placements can cause trouble. Sometimes less intuitive horizontal placements are smarter. The term "platforming" refers to deliberately allowing temporary gaps or holes before clearing a line above.

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Lying low

Find a spot within the confines of the existing upstack. This may mean needing to create holes or gaps. A higher and neater surface often requires more pieces than the messy and low one.

In the below example, the messier method creates less upstack.






The first example shows extra stacking above the current highest occupied row. It needs four extra rows in the future.






Diagrams made with tage.