Tap to drop the swinging slab onto the tower. The swing switches axis every floor, overhang is shaved off the deck, and a crosswind arrives once you are high enough.
👆 Tap anywhere to drop ← All gamesStackup hands you a construction crane and one job: land every slab squarely on the one beneath it. What makes it a 3D game rather than a flat one is that the swing alternates axis on every single floor. One slab tracks left and right across the screen, the next slides diagonally away from you into the depth of the scene, and your eye has to re-learn the alignment cue each time because the two motions look nothing alike from a three-quarter camera. The deck you are aiming at is the only thing keeping the tower up, so overhang is not a cosmetic penalty — whatever hangs past the edge is sheared off and tumbles away, and the surface you get to aim at next time is permanently smaller.
Tap anywhere on the canvas to release the slab; the space bar does the same on desktop. A gold marker on the deck below shows exactly where the slab will come down, and it turns grey for a fraction of a second after each drop while the crane resets — taps during that window are ignored, so hammering the screen does not help. Magnetic clamps forgive a small overhang for free, which is why the tower does not crumble on your first sloppy floor, but every miss past that tolerance shaves the deck and nudges its centre toward where you dropped, so errors compound in one direction. When the deck falls under the minimum width the tower topples and the run ends.
At thirty points a crosswind picks up. The swing is no longer centred on the tower — its midpoint drifts sideways on a slow cycle shown by the arrow in the corner — and the clamps tighten, so the free tolerance you have been leaning on shrinks. Dropping on the beat that worked in act one will now consistently land you off-centre, and you have to read the drift instead. Three consecutive near-perfect drops start the combo multiplier, and perfect drops actually widen the deck back out by a few units, so a skilled run can rebuild a tower it has been wearing down.