Ice Titan: Equip the ability "Gaurd". Now when the battle starts, whatever you do, DON'T USE AERO/AERORA/AEROGA!!! That will only make thos icicle things bigger! What you want to do is, when he shoots the icicles, use guard by pressing square (Make sure you dont have any other abilities that function using square, like dodge roll, eqipped). This will deflect the icicles back at him, hitting him in the face. THE FACE IS HIS ONLY WEAK SPOT!!! After a couple times of hitting is icicles back at him, hell go unconsious for a few seconds. So, glide/superglide ove to his face, and go ballistic. Ragnarok is especially helpful, but if you cant use it, then just go spaztic with the keyblade. Repeat these steps, keep an eye on your health, bring plenty of ethers and elixers, and you'll beat the ice titan soon enough.
Sephiroth: This is near to impossible unless you're lvl 75-100 and have Ultima Weapon. Make sure you have whatever Aero and Cure spell you have on your magic shortcut. Start off the fight by casting Aero and then charge at him. KEEP AN EYE ON YOUR HEALTH!!! Sephiroth can kill you easily. Also, make sure you always have Aero on. Now, it will look like Sephiroth isn't being hurt, but he is. Attacks like Ars Arcanum and Ragnarok are helpful, as is Gaurd. Make sure to bring elixers, and plenty of them. When he uses that pillar of flame, just use ars arcanum on him. It hurts him, and you dont get hurt from the fire! After you knock him down a bar, he'll start teleporting behind you and attacking, which can get quite annoying. Just keep Aero on. And also, Sephiroth will start using "Sin Harvesting". SIN HARVESTING CAN KILL YOU INSTANTLY(unless you have the ability second chance, in which case you have 1hp and no mp)!!! This is where those elixers come in handy. However, this attack can be easily stopped. Wenever you hear Sephiroth say "Sin Harvesting", glide over to him, and bash him with your keyblade. This will stop the attack, and he'll use the flame pillar instead. After a bith more damage is dealt, Sephiroth will get all this blue stuff around him, which causes blue orbs to come out of his attacks. They don't do much damage, but they get annoying. Just remember Aero. After a little while of dealing with that, Sephiroth uses his ultimate attack: SUPERNOVA! If you played FF7, you know how devastating this is. The attack causes several floating meteors to fall from the sky. But those arn't the SuperNova. As the meteors fly around hurting you, Sephiroth is channeling the SuperNpva, which can clearly be seen above him. DO NOT APPROACH SEPHIROTH!!! You cant hurt him during SuperNova! After a couple seconds of dealing with those meteors, the SuperNova explodes, causes massive damage. This is why we always use Aero, and have elixers to heal with. The remainder of the fight should be pretty simple. Sephiroth will use his array of annoying sword moves, but no more fire pillar, and NO MORE SUPERNOVA! Just keep an eye on your health, always use Aero, and Sephiroth will be dead before you know it.