Flat Spin is a skill that appears exclusively in Dragon Quest Tact. It is one of the Robo-robin's signature abilities, soaring forward at high speed and stunning any enemies in its flight path with a wind-infused thrust.
Flat Spin can be learned by Robo-robin at level 42 and costs 28 MP to use. It inflicts 160% potency Woosh-type physical damage to all enemies in a straight line of three squares in front of it, has a chance to stun them, and moves it forward up to four spaces.
A flat spin is a term in aerodynamics in which an aircraft's nose is pointed towards the horizon, sinking towards the ground with no forward speed. It can be very hazardous as the aircraft is typically unresponsive to any control inputs, being nearly impossible to recover from.