What it is. A second jump the player triggers mid-air, after the first has already committed them to an arc. One button, two impulses, one refill rule.

Player fantasy / why it’s fun. The apex is no longer a verdict. You leap, misjudge, and save it — the double jump converts a botched commitment into a mid-flight negotiation. It reads as competence you didn’t have to earn twice.

The verb

Press jump while airborne to spend a second impulse, resetting vertical velocity to a new upward burst. The whole design lives in when the charge refills.

How it feels / why it’s fun

• Recovery. The first jump is a bet; the second is the hedge. This is the single largest reduction in perceived difficulty you can add without touching level geometry — see pattern-anti-frustration and system-grace.
• Expression. Two impulses = a small vocabulary. Players route their own lines (early-double for distance, late-double for a stall-and-drop) — the seed of a pattern-mastery-and-flow curve.
• Legibility tax. Every extra air action is a thing the player must feel they still have. If the charge state isn’t obvious, air control becomes a guess — an antipattern-input-lie.

Tuning levers

Refill rule is the whole game. Ground-only refill keeps tension: you have two, never three. Wall-refill (as in anchor-celeste‘s dash economy) turns walls into gas stations and rewards route knowledge. Pickup-refill (floating charge orbs) makes the double jump a level resource, not a stat — now the designer places tension deliberately.

Height ratio: the tension dial

• 1.0× (equal jumps) reads as “you can basically fly a little.” Generous, floaty, forgiving. Good for cozy or exploratory traversal.
• 0.6–0.8× (shorter second) reads as a save: enough to clear a lip you undershot, not enough to trivialize a gap. This is the precision-platformer default.
• >1.0× (bigger second) teaches players to deliberately waste jump 1 to load jump 2 — a nice twist, a bad accident. Only ship it if it’s the point.

Slots into

• genre-precision-platformer — the canonical home; pairs with tight system-camera-and-controls and a merciless system-save-and-checkpoint.
• genre-metroidvania — a classic gated traversal upgrade; withholding the double jump is the map lock (Metroid, Hollow Knight’s Monarch Wings).
• genre-puzzle-platformer — when refill is a placed resource, the jump becomes a spatial puzzle piece.
• genre-physics-arcade and genre-action-adventure — air agency without full flight.
• Anchors: anchor-celeste, anchor-dead-cells, anchor-spelunky (the cape/climbing gloves as air-agency cousins), anchor-braid (jump-on-enemy chaining).

Twist seams

• Double jump but the second one costs a held resource (constraint). Jump 2 drains a stamina/mana/heat bar you also spend on other verbs. Now every save is a budget decision, and the system-economy reaches into your traversal — see pattern-risk-reward.
• Double jump but jump 2 is a downward stomp, not an up (mechanic-swap). The second press slams you earthward — offense and fall-control fused into one air option. This is mechanic-ground-pound wearing the double jump’s slot; it inverts the recovery fantasy into a commitment.
• Double jump but the second refills only on hitting an enemy (constraint). Air chains become mandatory combat lines à la anchor-nuclear-throne aggression loops — the floor is lava and mobs are the only refuel.

How it wires to Hayao

• The double jump is a state machine on an air-charge counter: grounded → set charge; airborne + press + charge>0 → apply impulse, decrement. Keep the counter in sim state so it lands in the world hash; render the “have a charge” tell as a pattern-readability cue.
• Read the platformer motion lab / sandboxes/ movement lab for jump-arc math, coyote time, and input buffering in isolation — don’t reinvent apex tuning inside a full game.
• The gated-upgrade version (metroidvania) is progression, not physics: model the unlock as a flag in your system-progression / worldgraph, provable like any other lock.
• Feel and forgiveness are proven downstream — the frontmatter’s verify-with (design/FUN.md precision-platformer) and Channel-4 feel gates own that. Design the rule here; prove the arc there.

Fails when…

• Charge state is invisible. Player can’t tell if they have the second jump → every air moment is a coin flip. Fix with an unmissable tell (sprite state, dust puff, meter) — pattern-readability.
• It erases the level. If jump 2 clears everything jump 1 was designed to gate, your platforming collapses into hold-right — an antipattern-boring-optimal. Geometry must assume the second jump exists.
• Refill is too generous. Air-refill with no cost = flight. If you wanted flight, ship mechanic-glide or a mechanic-swing, not an infinite ladder.
• The second is a strict repeat of the first. Two identical impulses add reach but no decision. Differentiate via height ratio, stomp-swap, or a cost.
• Buffer/coyote missing. Frame-perfect double jumps read as an antipattern-input-lie; the player pressed, the game shrugged.

See also

• Air-agency siblings: mechanic-wall-jump, mechanic-dash, mechanic-glide, mechanic-wall-run, mechanic-ledge-grab, mechanic-bounce, mechanic-gravity-flip.
• Swap target for the stomp twist: mechanic-ground-pound.
• Forgiveness + tuning: system-grace, pattern-anti-frustration, pattern-mastery-and-flow, system-mastery-curve.
• Where it lives: genre-precision-platformer, genre-metroidvania, system-camera-and-controls.