DOWNSTACKING & DEFENCE · LESSON 2 OF 3
Finding the route
AFTER THIS GUIDEYou can connect a current clear to a second reachable target and explain when a small skim is worth taking.
Plan two clears, not just one landing.
A downstack route is a sequence of access changes. Clear the upper row or group, inspect what survives, then reach the next hole. The best first move is not always the move that clears the most lines immediately.
Use the visible queue to test the route. Imagine the board after the first clear, including every leftover cell from the placed piece. Ask whether the next piece can reach the new target without sealing another gap.
Sometimes a small skim is the entry fee. Completing a row above the garbage can remove a roof and expose the channel. That differs from repeatedly building higher because you have not read the route.
Do not require a combo from every dig. Consecutive clears are useful when they arise from reachable placements, but protecting the next hole matters more than forcing an immediate clear that traps it. A quiet placement can be the bridge to a better continuation.
Account for what the clear leaves
Start from an accessible channel
The downstack sequence has three aligned garbage holes. A vertical I reaches all three, so the first clear is easy to identify.
Count the residue
I contains four cells. Only three of its rows disappear. Advance the diagram and find the one surviving cell; do not mentally erase the whole piece.
Apply the same check to a skim
The skim illustration removes a high row above lower space. Ask which old blocks move down and whether the next hole remains accessible. Plan the next piece on that new surface, not the old one.
The channel is open from above.
A vertical I completes three garbage rows.
The garbage is gone. One cell remains, so this is not a Perfect Clear.
A small clear can lower the stack and preserve access to a well instead of waiting for a larger attack.
Common mistakes
Planning on the pre-clear heights
Every surviving block above a cleared row falls by one row under normal line-clear gravity. Your next landing must use those new heights.
Always saving I for four lines
A timely I Triple or smaller clear can expose a route. Saving it may force extra blocks over the very channel you need.
Covering the next hole to finish the current row
Sometimes a necessary tradeoff exists, but recognise the cost. Compare an alternative that leaves the next entrance open.
TAKE IT TO THE BOARD
Three two-clear plans
- Use Downstacking, Gravity Off and NEXT 5. Slow the garbage interval while studying.
- For three positions, predict the board after a clear and name the next target. Include leftover cells from the active piece.
- Execute the plan. If it fails, inspect the earlier placement with Undo or Game history and identify what blocked the route.
What counts as progress? You describe two reachable clears and can explain the residue between them.
Open practice ↗Opens the mode. Set Gravity and NEXT yourself; your current settings are kept.
Keep these terms nearby
NEXT IN THIS PATH
Tank or cancel?
Weigh accepting garbage against cancelling it; rules vary by game.
Read the next guide →Further reading
For setup variations and additional examples, see How to Tetris: Downstacking. The practice task here is original to Stacking Lab.