Land the marble inside the window.
Not fastest — exact. Every one of the 150 levels gives you a piece budget and a target like 7.80–8.20 seconds. Bolt the run together one piece at a time, drop the marble, and stop the clock inside the window.
Accelerators
Polished brass chutes, ramps, drop tubes and booster pads pile on speed.
Decelerators
Rubber friction pads, spinners, funnels and switchbacks buy you time.
Utilities
One-shot gates, rotor bars, narrow gaps and teleport pairs for the late levels.