Well this is just an amazing surprise from Sakurai.
In celebration of the coming release of Sephiroth on December 22, Super Smash Bros. Ultimate will have temporary boss fight event with Sephiroth right now. It is split into three difficulties with Very Hard being the hardest. This is a celebration of Sephiroth’s last boss status. So before you use the One-Winged Angel, why not go against him till then? Note that the event will only run for five days leading to Sephiroth’s release on December 22, 5 PM PT. So if you want to face the original final boss of Final Fantasy 7, be sure to update the game and get in before then. For he will never be a memory soon enough.
Here is my personal best. Be warned, he is no joke.
After you beat him in Very Hard mode, you can use Sephiroth after.
Super Smash Bros. Ultimate is available now for Nintendo Switch.