What it is. The player adds pieces to a vertical structure that must not fall. Each new piece raises the score and lowers the margin — the tower that earns you points is the tower that kills you.

Player fantasy / why it’s fun. “One more, I can balance it.” Growth is visible, precarious, and self-inflicted. You are not fighting an enemy — you are fighting the thing you built, and every point is a debt against gravity.

The verb

Place, drop, or fling a piece so it settles on what is already there — then decide whether to push your luck with another.

How it feels / why it’s fun

• Legible jeopardy. A leaning tower telegraphs its own doom; the player reads risk with their eyes, no UI. See pattern-readability.
• Self-authored tension. The difficulty curve is the player’s own greed. Height is both the reward and the threat — a pure pattern-risk-reward engine.
• The wobble is the whole game. Instability must be felt before it’s fatal: sway, creak, a lean that recovers. That anticipation is the juice — pattern-pacing-and-tension.

Tuning levers

Default to the wobble model over pure snap: instability is where the fun lives. Reserve snap for grid-puzzle framings where the tension comes from footprint, not physics.

Slots into

• genre-physics-arcade — the native home; toppling towers, one-more loops.
• genre-incremental — height as a resource you spend and rebuild; see system-resource-loops.
• genre-grid-puzzle — snap-stacking where the puzzle is packing, adjacency, and footprint.
• genre-tower-defense — literal towers whose reach scales with a stacked base.
• genre-coop-chaos — two hands on one tower; see system-coop-and-competition.

Anchors worth studying: anchor-tetris (packing pressure, line-clear as controlled collapse), anchor-katamari (accretion as growth-is-power, growth-is-unwieldy), anchor-peggle (physics arcade juice on a single satisfying act), anchor-minecraft and anchor-terraria (stacking as construction, not jeopardy — the calm end of the spectrum).

Twist seams

• Stack but the tower is your health bar (mechanic-swap). Damage removes pieces from the top; you heal by stacking under fire. Losing height is taking a hit, so building and surviving are the same verb. Pairs with system-combat-model and pattern-feedback-loops.
• Stack but the pieces are your defeated enemies (theme). Every kill drops a corpse you must place; a good run builds a monument, a bad run buries you. Reframes system-enemy-archetypes as building material and ties score to combat — see world-motif-and-symbol and world-theme-vectors.
• Stack but gravity flips on a timer (mechanic-swap). The tower you balanced upward must now hang stable downward. Composes with mechanic-gravity-flip and forces the player to build symmetric, defensible structures.

How it wires to Hayao

• Use a deterministic physics step so a given seed of piece order and drop timings always collapses the same way — proofs and replays depend on it. Read the physics-lab under sandboxes/ for the rigid-body seam and how contact resolution stays reproducible.
• For the snap / grid framing, model the stack as a pure Puzzle<State, Move> (footprint occupancy + a stability predicate) so every layout is machine-checkable and levels are provably clearable — the examples/sokoban/ split is the reference for logic-vs-view.
• The wobble, dust, and creak are cosmetic: sway animation, particle puffs, and shake read as pure-view and must stay out of the sim hash. See pattern-juice-choreography.
• Score, current height, and collapse are logic state that lives in the hash; the lean animation is not. Keep the boundary clean or replays desync.
• Verification lives in design/FUN.md#19-·-physics-arcade — prove the collapse is fair and the wobble reads before you tune the greed curve.

Fails when…

• The collapse feels random, not earned. If the player can’t see why it fell, jeopardy becomes noise — the antipattern-rng-frustration and antipattern-input-lie trap. Telegraph the lean; let the eye predict the fall.
• Snap-stacking with zero instability. No wobble, no packing pressure = you’ve built a stacking animation, not a game. That’s antipattern-false-depth: the verb has no stakes.
• Height with no ceiling on tension. If a tall tower is strictly safer than a short one (better base, more mass), greed stops being a gamble and the loop goes flat — antipattern-boring-optimal.
• Full collapse with no grace. Wiping a 40-piece tower on one bad drop is a rage-quit; offer lose-top or a checkpoint. See pattern-anti-frustration and system-grace.
• Too many piece shapes too soon. Variance before the player masters the base verb reads as chaos, not challenge — respect the system-onboarding ramp.

See also

• mechanic-throw — the delivery verb when pieces are flung, not dropped.
• mechanic-merge — the sibling growth loop: combine-to-grow instead of pile-to-grow.
• mechanic-grow-shrink — scale as the tension axis rather than height.
• genre-physics-arcade, genre-incremental, genre-grid-puzzle — the three homes.
• pattern-risk-reward, pattern-pacing-and-tension — the tension spine.
• recipe-merge-factory — a build-and-grow loop you can cannibalize for structure.
• process-the-twist — where the “X but Y” seams above come from.