Cannot be Normal Summoned or Set. Must be Special Summoned by "Yubel", and cannot be Special Summoned by other ways. This card cannot be destroyed by battle. You take no Battle Damage from battles involving this card. Before damage calculation, when this face-up Attack Position card is attacked by an opponent's monster: Inflict damage to your opponent equal to that monster's ATK. During your End Phase: Destroy all other monsters on the field. When this face-up card leaves the field: You can Special Summon 1 "Yubel - The Ultimate Nightmare" from your hand, Deck or Graveyard.
Okay confirmed lol. You literally can win with whatever deck you want as long as you have more cards than her and you never summon any monsters. Of course that gives you a really shitty duel assessment so if you want better rewards you need to find a way to beat her for real, but if you just want to complete the relevant missions and get the Terror Incarnate card stalling her out works just fine.
"Ante " spell is the most important problem with Yubel Lvl 50:
"Each Player reveals 1 card from their hand. If one card is higher Level than the other, the card with the lower Level is sent to the Graveyard, and the player who revealed it takes 1000 damage. (Non-Monster Cards are treated as Level 0.)"
I think i need some good traps like: Magic Jammer or Ultimate Providence or something like that to counter it. Or just play with Silent Swordsman
I just accidentally stumbled across a great way to cheese this fight. I played reptillane viper, wanting her to kill it so I could use tokens to summon Ra, and got control of Yubel. I had Showdown of the Secret Sense Scroll Techniques already down when she destroyed it with Tribute to the Doomed, so she didn't get to summon her final form. Not what I intended to happen but it worked out.