Cannot be Normal Summoned or Set. Must be Special Summoned by "Yubel - Terror Incarnate", 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. At the end of the Damage Step, if this face-up Attack Position card battles with an opponent's monster: Inflict damage equal to that monster's ATK to your opponent, also destroy that monster.
Personally, I beat her by just doing nothing, just pass my turn. Same for the yubel 50. Easiest lvl 50 & 60 of duel links x)
The whole Yubel fight thing was very easy for me at least because all you really need is like a dark valkyria or Zaborg the thunder Monarch to get rid of the Ultimate nightmare or any card that destroys a monster, or just get lucky and not summon any monsters and use a de spell to get rid of the field spell. Also if you want you could just keep a terror incarnate in your deck so the ante card doesn't work.
literally filled my deck with just spell and trap negating and destroying cards and then chain destruction and just sat back an watched Yubel deck out. No monsters in deck win. Once Yubel has no field spell, there is nothing it can do.
after 5 loses,I realized level 60 never summoned any other monsters. So, I stalled by filling my deck up with cards that increased my LP and low ATK monsters, so not to take too much damage from Ultimate Nightmares effect...and won the very next match due to Yubel not having any cards left.
I usually use Twin Fusion Dragons, and I just slapped 2 Enemy Controller, 3 Dien Keto the Cure Master, and 3 (I can't remember the name, but it heals 600LP a use.), and just stalled out Yubel to deckout.