To reach the URA battle (special battle) in the Battle Arena, first gain 64000 battle points and purchase the W-Summon materia. Then, get 32,000 battle points and buy Cloud's level 4 limit, Omnislash. Equip Omnislash and speak with the lady at the counter in the battle arena, and she will ask you if you want to participate in a special battle. Defeat all 8 enemies and get the Final attack materia. Note: You must have your Ultimate Weapon equipped to fight in the special battle.