This study presents a swift, agile, untethered millimetre-scale soft propulsor inspired by the Stenus comma beetle. The propulsor, with a body length of 3.6 mm, achieves a specific speed of ~201 BL/s and acceleration of ~8,372 BL/s², surpassing previous soft robots at similar scales by several orders of magnitude. It demonstrates on-demand braking with a deceleration of ~-5,010 BL/s² and exhibits comprehensive kinetic performance comparable to natural insects. The propulsor is designed by systematically mimicking the beetle's flexible abdomen, secretion transport canals, and body setae, combined with magnetic-induced fast posture transformations. The propulsor uses a bioinspired real-time magnetic-triggerable tail for propulsion material delivery, precise surfactant release for surface tension gradient control, and effective braking hydrodynamics. The design enables agile motion with high acceleration, velocity, and deceleration, and it can mimic the beetle's escape behavior from predators. The propulsor's performance is validated through experiments and simulations, showing its potential for real-time trajectory control and dynamic maneuverability. The study highlights the importance of systematic bio-inspiration in achieving over-biological performance in soft robotics, offering new insights for robot design, optimization, and control paradigms. The research also identifies key challenges, such as the need for real-time sensing and feedback, and suggests future directions for integrating advanced sensing systems and selective manipulation strategies. The work demonstrates the potential of bio-inspired soft robots to revolutionize robotics by achieving unprecedented performance in dynamic environments.This study presents a swift, agile, untethered millimetre-scale soft propulsor inspired by the Stenus comma beetle. The propulsor, with a body length of 3.6 mm, achieves a specific speed of ~201 BL/s and acceleration of ~8,372 BL/s², surpassing previous soft robots at similar scales by several orders of magnitude. It demonstrates on-demand braking with a deceleration of ~-5,010 BL/s² and exhibits comprehensive kinetic performance comparable to natural insects. The propulsor is designed by systematically mimicking the beetle's flexible abdomen, secretion transport canals, and body setae, combined with magnetic-induced fast posture transformations. The propulsor uses a bioinspired real-time magnetic-triggerable tail for propulsion material delivery, precise surfactant release for surface tension gradient control, and effective braking hydrodynamics. The design enables agile motion with high acceleration, velocity, and deceleration, and it can mimic the beetle's escape behavior from predators. The propulsor's performance is validated through experiments and simulations, showing its potential for real-time trajectory control and dynamic maneuverability. The study highlights the importance of systematic bio-inspiration in achieving over-biological performance in soft robotics, offering new insights for robot design, optimization, and control paradigms. The research also identifies key challenges, such as the need for real-time sensing and feedback, and suggests future directions for integrating advanced sensing systems and selective manipulation strategies. The work demonstrates the potential of bio-inspired soft robots to revolutionize robotics by achieving unprecedented performance in dynamic environments.