GBVR Special boss fightm ((w/ Siegfried)
To achieve the boss fight you have to do 6 SBA/SSBA's (AKA ult) finishes for each battle (doesn't matter what difficulty). Then battle avatar Belial It took me a while but I think to get your SBA gauge up I recommend Lowain in case you miss your ult on the character. Also sry for my bad gameplay, I was focusing on the gauge for the finish ending and also not showing the card at the end because it's different for every character.