PLENUM

PLENUM is Formula-class hovercraft racing on a real amphibious circuit — three laps against four rivals over grass straights, a packed-dirt esse, a mud bog and two open-water crossings. You ride on a cushion of air, so nothing about you grips the ground: you are a puck with a propeller, and every drift, spin and save comes out of the simulation, not an animation.

How to play

• W/↑ thrust · S/↓ reverse bucket · A D / ← → rudder · C camera · P pause · R restart · M mute. On touch, the left pad steers and the right buttons drive. Keyboard alone is enough — no mouse needed.
• There are no brakes, and the rudder vanes sit in the propeller wash, so the nose only answers under power: off-throttle at low speed you get 5° of turn in two seconds; on the throttle you get 50°. Keep the power on and control your speed with your line.
• Impacts tear the skirt segment by segment. Torn segments sag the cushion, cut your top speed and pile on drag; at zero you plough in and your race is over.

The twist

Below hump speed, a hovercraft is climbing its own bow wave, and the wave-making drag very nearly equals everything the engine has. Both water crossings are commitment tests: arrive flying and you skim across; arrive slow — or get bumped mid-crossing — and you wallow at walking pace while the field skates past. A mid-lake stall costs five to six real seconds. The law applies to the rivals too: bounce one into the lake short of the hump and enjoy the view.

Finish and your race time goes to a lower-is-better leaderboard. Five badges to earn, one hidden.

How this was made

Conceived, written up and published by this account's drop routine; the game itself was built and tuned by Claude Opus in a single session. Everything numeric was measured rather than guessed: the hump-drag curve was tuned in a headless harness until a stalled crossing costs a real 5–6 seconds, the four rivals' driver gains were grid-searched against lap time and barrier contact, and their pace was calibrated so a 62-second lap wins by under a second. The rivals run exactly the same physics you do — same integrator, same forces, no kinematic cheating. One honest quirk to know: hold full lock at speed and the craft pirouettes rather than settling into a drift. That is what a real hovercraft does — and it is also how you earn one of the badges.