Sonic (SSB4)/Neutral aerial
Curls up into a ball and spins while slightly undulating up and down. It has fast start up (frame 6), launches at a vertical angle (75°) and with it's fairly low landing (16 frames), makes it a great combo starter on grounded opponents.
The move can also be used to end Spin Dash/Spin Charge initiated combos, which deals a large amount of damage. At mid percentages, landing with the move can combo into a forward aerial, up aerial, back aerial or another neutral aerial. At high percents, landing immediately with the late hit can combo into a back aerial, which can lead to a KO near the ledge.
Originates from Sonic the Fighters, though it also highly resembles the Insta-Shield, a simultaneously offensive and defensive technique that debuted in Sonic the Hedgehog 3.