Get at least two Mystical Sheep, Kajezin, and Monster Reborn. Summon Kajezin and wait until he summons Blue Eyes White Dragon. When he attacks, Kajezin uses Kajezin effect against his Blue Eyes White Dragon that makes its attack 0 and it will be destroyed. Then use Monster Reborn and wait until you get Polymezeration and two Mystical Sheep. Do not summon it, but instead activate Polymeziration. You can now use Blue Eyes Ultimate Dragon.