When sephiroth loses enough stocks and takes enough damage he gains one winged mode. Many factors determine this mode and give him various benefits. He gains super armour on all smash attacks, gains a 3rd jump, and does extra damage for his moves. It will only appear once each stock and disappear after he loses his current stock or takes a stock from the opponent.
Sephiroth's neutral B allows him to shoot projectiles. Holding the B button allows him to charge the projectile with 3 stages, the third being the most powerful. The last stage has the ability to kill at 0% and is a great punish option after a shield break.
His side B allows him to shoot projectiles again. It has 3 stages with an extra projectile at each stage. A maximum of 3 projectile can be shot at a target at a time but a target can take 5 projectiles. After the projectiles are stuck on the target they eventually smash into the target allowing for great edguarding methods and hype finishes.
Sephiroth's up B allows him to recover by slashing his sword. It had two stages if holding the B button. The first stage will cover decent distance and snap to the ledge while the 2nd stage will go a little bit past the ledge and not immediatly snap to the ledge.
The down B of sephiroth is a forward facing counter. While it leaves him susceptible from behind it will counter attacks dealing more damage than the attack that hit the counter. Unlike most counters though it will still attack even if not hit.