FOUNDATIONS · LESSON 1 OF 5
How a stack works
AFTER THIS GUIDEYou’ll be able to tell an open gap from a buried hole and explain why a piece that fits can still make your stack worse.
Read the empty spaces, too.
A stack is the collection of locked blocks on the board. Its surface is the outline a falling piece meets. That outline tells you where a piece may land, but it does not tell you everything underneath it. Before committing, look at both the landing and the empty cells below.
An open depression is not automatically a problem. A two-column step may be a useful O landing. A one-column well can be a deliberate route for a vertical I. The important distinction is access: can a suitable piece still reach the bottom?
A hole has a block somewhere above it in the same column, so a piece cannot simply fall straight into it. Some holes can be reached with a sideways move or rotation; others need covering rows cleared first. For your first stacking drills, avoid creating holes you cannot explain how to fill.
An overhang is a ledge extending above empty space. Later, you will build deliberate overhangs for spins. For now, a roof without a known entry is a warning, not a clever setup.
Judge the next few landings and the access underneath them. A useful step is fine. A tidy-looking roof over an unreachable gap is not.
WORKED EXAMPLE · ONE O, TWO CHOICES
Check what the landing covers.
These are six-row bottom slices, with columns numbered one to ten from left to right. Grey blocks are locked. The same O can land in either position below; the consequences differ.
Find the supported step
Columns eight and nine have room for an O. Both have blocks below the empty area. Column ten is the deliberately open well.
Fill the step
Place O in columns eight and nine. Every new block has support through its piece or the stack. The right well remains open, with four rows waiting for I.
Compare the tempting alternative
Start again from the first board. Move O one column farther right. It still lands, supported by column nine, but its right half roofs over two empty cells in column ten. A vertical I can no longer reach the bottom.
Try explaining the difference without saying “flat”. The first placement preserves a route for I. The second closes that route. That is the decision you want to notice during play.
Common mistakes
Looking only at the ghost outline
The ghost tells you where the current drop lands. It does not promise that the landing leaves a good board. Check below every part that sticks out.
Treating every gap as a hole
An open well is useful space. Filling it just because it looks empty can remove your easiest clear. Ask what the gap is for before covering it.
Saving a bad roof by building higher
Adding blocks above a buried gap usually adds work before you can reach it. If you create one, look for a small clear that exposes it rather than hiding it under a larger stack.
TAKE IT TO THE BOARD
10 pieces. Name the space you leave.
- Set Gravity to Off and NEXT to 5. Keep Auto Play off so you make the placements.
- Before each of ten locks, identify the well and one other possible landing. Look beneath the ghost.
- After locking, check whether you created a hole. If you did, use Undo once and compare a different placement.
- Finish by pointing to one useful step and describing which visible piece could use it.
What counts as progress? You notice an accidental roof before dropping, and can distinguish a deliberate open channel from an inaccessible gap.
Open 9–0 practice ↗Opens the mode. Set Gravity and NEXT yourself; your current settings are kept.
Keep these terms nearby
NEXT IN THIS PATH
Reading the queue
Use the next pieces to decide which useful spaces to preserve.
Read the next guide →Further reading
These board examples and drills are original to Stacking Lab. For another perspective on keeping a stack playable, see Galactoid’s How to Tetris: Stacking.