Goodhart
An infinite, one-button game about a number: tap and it climbs, while what it measured drains unseen.
Tap. The number goes up.
One button, and the number only ever goes up. Tap fast, less than 0.4 s apart, and a streak multiplies every tap.
Behind the number is the value it was meant to measure, never shown while you play. A slow tap adds to it. A fast tap never pays for its own interval. When the value reaches zero the run is over, mid-climb and without warning.
Nothing gets harder. The rules at the first tap are the rules at the last.
The card sets the number beside what it measured, and beside a steady hand tapping twice a second.
Canvas2D, so the game is whole on any phone. No camera, no account, and nothing leaves the machine.