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: Tribute 1 other monster or destroy this card. When this card is destroyed, except by its own effect: Its owner can Special Summon 1 "Yubel - Terror Incarnate" from their hand, Deck, or Graveyard.
Destroys any monster that battles with her and inflict damage to your opponent equal to that monster's attack.
Requires a tribute every turn to stay on the field.
Can be costly to summon.
Yubel has 3 forms each stronger than the last and needing the previous to be summoned. The best way to special summon the original Yubel is with Limit Reverse so that you can easily destroy it by switching battle position turning it into Yubel - Terror Incarnate which needs no cost to stay on the field. Yubel - Terror Incarnate destroys every monster on the field during your End Phase. If for any reason Yubel - Terror Incarnate leaves the field you can then special summon Yubel - The Ultimate Nightmare which destroys any monster it battles and inflicts damage to your opponent equal to that monster's attack.
Yubel has no inherent special summoning condition and tribute summoning her might be difficult and costly. You can ease the summoning by using Mausoleum of the Emperor and paying 2000 LP to summon her instead.
Summoning her from the graveyard might prove to be the most effective method if you have a way to get her there in the first place. You can use cards like Archfiend Call and Damage Gate to revive her. Overdone Burial and Limit Reverse revive Yubel and give you options to destroy her and summon her higher forms. Change Yubel to defense position while attached with Limit Reverse to destroy her. With Overdone Burial Yubel's effect on the field is negated meaning she can be destroyed by battle, but when she hits the graveyard she will no longer be affected by Overdone Burial allowing you to upgrade her.
I didn't test this so I'm not sure but Slifer's effect doesn't say original ATK so I think if "?" ATK monsters don't have any ATK when they're summoned (like Winged Dragon of Ra) they'll behave like Yubel but monsters like Evil Dragon Ananta and Chimeratech Overdragon are summoned with ATK points, so they would lose ATK by Slifer's effect and get destroyed if their ATK is low enough
Fire King Avatar Yaksha and destroy Yubel in your hand :)
You could use Black Ptera, Peten the Dark Clown, or Kujakujaku to ease the cost for keeping this card on the field. Battle Mania, Staunch Defender, and All out Attacks or Savage Colosseum (if they come out) would make this card's effect inflict plenty of damage.