Tap, click or press Space. Tap again in the air for a double jump.
The whole game is one file: william/pages/runner/game.js. The top of it is a list of dials.
Set GRAVITY to 1200 and reload. Moon jumps. Set AIR_JUMPS to 3. Set WALL_CHANCE to 0.8.
Nothing you change here is permanent. Break it on purpose.