Zeromus
HP: 110,000
"WHOA that background is dizzying! The various friends in your quest will give you their life, strength, vitality, and hope, completely restoring your HP and MP and curing status effects. Once this is passed, and your party is ready to go, DO NOT FIGHT! Nothing will affect him in this big blue state...so keep parrying until Edge can steal a Dark Matter from him. You'll need this later, trust me. Now, have Cecil use the Crystal, which will break Zeromus' effect.....but revealing his true form, this big nasty monster that needs the righteus hell beat out of him! Zeromus has a myriad of spells that he uses, most often being Flare and Meteo, but they don't do the big damage one would expect, but his Flare can be crippling. More devastating is the Big Bang, where Zeromus changes the spin of the world and causes great damage to everyone in the process. However, if you have the Dark Matter like you should, this won't be too much of a problem. Now, Rosa can cast Haste on Cecil, Kain, and Edge to speed up their attacks. After this, she should do nothing but alternate with Holy on Zeromus and Cure4 over the party. Rydia should alternate casting Flare, and summoning Bahamut. Edge should throw whatever he can throw, especially swords and the Spoon Dart, if you have it. When he's out of things to throw, keep attacking normally. Kain should do nothing more than jump and jump and keep jumping. Cecil should keep attacking with the Crystal Sword. All I can say is, keep the HP's up with Rosa, and use Elixirs whenever necessary. This will take a while, but soon enough the lightning will flash, and Zeromus will begin his dissapation into nothingness.
Congratulations, you've done it! Now, sit back and enjoy the lengthy ending."
Quoted from a higher power :]