... https://www.youtube.com/watch?v=KUWMh0v2iBU

This took literally 10+ hours to do. I didn't have the correct layout at first and honestly didn't have it when I finally beat him. Party Layout: Tifa (Leader), Cloud, Aerith Materia and Weapon Layout: Tifa: Elemental + Wind, Parry, HP Up, MP Up, Luck Up, ATB Boost, Steadfast Block Cloud: Elemental + Fire, Carbuncle Summon (To Avoid Instant Death since I don't have enough levels on HP Up), Raise Aerith: Magic Up, Magic Up, Magnify + Time, Synergy + Fire (Level 1 Fire Attacks automatically are cast after doing a special attack with the party leader. This is invaluable with the second phase). Here is my strategy: First phase: use Tifa to parry (slide) under and around his attacks while Aerith and Cloud cast level 3 magic spells on him, which stun him. I then used Tifa's power up attacks, punches, Chi Trap, and Focus Attack attacks to damage him. Do this enough until you stagger him. Second Phase: At the end of the stagger, use Aerith to case Arcane Ward and use all 3 characters to cast Level 2/3 magic attack at the start of the fight. This phase is immune to physical attack except when you equip Elemental materia. Keep attacking him with magic and physical Elemental attacks until you stagger him or he switching phase. Switch Back To First Phase: Immaculate End can instantly kill you if you don't have barrier and enough HP to survive it. I just equipped Cloud and Aerith with Revival Rings and used Carbuncle to heal and revive everyone. Tifa has Reprieve so she comes back if she is incapacitated from a non-9999 death. Carbuncle automatically revives everyone at the end of the summon if they are KO'd. What's annoying is that Weiss will murder you if he switches back to his third phase and you are getting back up, since your ATB resets. Third Phase: Weiss recovers his health and devastating attacks, but can be easily staggered with limit breaks and fast physical attacks. Stagger him quickly but you likely want to use Cloud or Tifa's stored limit breaks quickly right after the first hit since he can teleport in the middle of your Limit Break animations. I honestly got lucky that he went back to his second phase at the end since he isn't much of a threat. I didn't have True Strike with Tifa nor the Fury Rings. ... https://www.youtube.com/watch?v=jm2VQipP-wM