Sigma is not to be bound by gravity like other beings. Now, he needn't be.
Sigma may now untether himself at any time from gravity by pressing jump. Once untethered, Sigma can move freely in three dimensions. To make him easier to control, additional controls have been created for his untethered state. Holding the interact key locks Sigma's altitude, allowing him to hover at a consistent height, while tapping jump again nullifies all momentum, allowing Sigma to hover. (Note: hover is extremely finicky at times. If Sigma fails to fully stop, tapping jump again should stop him.)
Sigma may return to his tethered state at any time by pressing the crouch button. Once retethered, Sigma acts as normal, useful in vertically tight spaces, for when flying may not be the best option, or for rapidly losing altitude.