Downstacking

Downstacking refers uncovering and filling holes in order to gain access to the bottom rows of the stack. 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.

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


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.





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.





Clearing 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.


Finding Line Clears

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. Get creative.



















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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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Prioritizing Line Clears

If there is a placement that will clear a line and uncover a hole, then there is a strong chance that it is a good move. The next-coming pieces may be the ones that you need to address the next-coming hole. Waiting to open up the hole may mean that you must sideline those pieces and waste the opportunity, as well as risk needlessly stacking above a hole down the line.

Our goal is to use as few pieces as possible to uncover all of the holes. This is logically the same as maximizing the lines-to-piece ratio from the start to the piece that uncovers the last hole. 

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Problematic Patterns

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.



Crowding

By directing upstack residue away from upcoming holes, you create 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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Diagrams made with tage.

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