For the early game in Kingdom Hearts I spent a lot of time dying and having to restart. Boss fights were killers but I'd often die to just random dudes. The game is non-punishing in that it restarts you in the previous room with all experience and loot gained from everything except the fight that killed you which is nice. Eventually I reached the point where dying was no longer something I could really do. Part of it I'm sure was getting better at the game and knowing how to avoid damage and when I needed to be healed, but part of it was also leveling up and getting more abilities. Second chance was the big one, where you get set to 1 health when you would die instead of dying which gave you a chance to heal up before taking another hit. There's a small delay in casting the healing spell but it was generally fine. Perhaps even more important was gaining inevitability. I learned an ability which gave me back mana when I took damage. Enough mana that I could constantly heal myself back to full after taking any damage at all! So playing safer and always healing coupled with not being able to get one shot coupled with experience with the game all combined to be essentially invincible.
Then I unlocked the Sephiroth fight. His attacks would hit me for about 60% of my max health and were essentially instant so there was no chance to respond. I could run away pretty well and it still took 3 hits to kill me but most of my time was spent running and healing and very little was spent trying to do damage. He also has an AE attack that hit everyone around him twice... That would put me to critical if I ever made a misstep and got caught in it. I played him a few times and eventually got the hang of not getting caught in it. I also learned his movement and attack patterns and was able to pretty consistently get in for a small amount of damage. I fought him for about 12 minutes and was starting to get cocky. I was on autopilot enough that I started writing a blog post about how easy he was. Then I got him down to a set amount of health (halfway through the pink bar I think) and his pattern changed. He teleported away, started chanting a spell, and then I got knocked to 1 health and 0 mana. My infinite play plan involves casting the heal spell which costs 1 mana... I can't cast it now! Oh, and Sephiroth immediately charged me after doing this and killed me.
Ok... Fine. Kingdom Hearts has items but you have to equip them before a fight and you're limited by how many item slots you have. I can equip 6 items so I put on 6 elixirs (full health and mana) and gave him another try. 12 more minutes and he changed phases again. I was able to drink my elixir and heal to full before he charged me. Yes! He was in a new attack pattern though, one that didn't seem to have the easily exploitable gaps for damage that the old one had. It also attacked much more frequently which was making it hard to stay healed and really gave no chance for offence, but that's fine... And then he teleported away and knocked me back down to 1 health and 0 mana. I'd been hoping it was just a phase change thing but no... He will repeatedly make me use an elixir over and over until I run out or I kill him it seems. And I was not going to kill him.
Was there some trick to this? I could turn to the internet to find out but I knew I could get a lot more powerful by gaining some levels and crafting some permanent stat boosts. So I wandered away to gather a ton of crafting materials and incidentally gain levels. In the process of doing so I had to look up where some of these things dropped and actually learned what some of the summons I'd never used could do. Turns out Bambi gives you infinite mana and drops crafting materials as you kill enemies based on what zone you're in! So I could just run in a circle spamming thundaga and get tons of loot. Most of the good stuff required some specific rare drops and one item required farming crazy mushroom dudes but I ended up making the Ultima weapon and something like a dozen strength and defense pots.
Back to Sephiroth... It turns out casting my protect spell to halve incoming damage along with having twice the max health and a lot of extra defense made a big deal to how much damage he could do to me. My first time around I had to spend a lot of time running away and healing. This time around I could take 3 hits without fear and then think about healing. I also seemed to be doing probably quadruple damage from the previous time so I could hit the phase change in a minute or two instead of a dozen minutes. It turns out power leveling your stats matters!
I was still having trouble dealing with running out of elixirs since I couldn't really find a good window to do damage in the second phase. Then at one point he teleported beside me to use his instant death attack and I attacked him while he was chanting. It interrupted the chant! And gave me a window to do a bunch of damage! Woohoo! Then I died a few times figuring out how far away I could be and still interrupt him. I was dead any time I failed because he'd knock me to 1 health and I'd be standing beside him which didn't give enough time to drink an elixir. So I ended up in a situation where if he randomly warped close to me I could hurt him, and if he randomly warped far away from me I'd lose one of my 6 elixirs. So I fought him over and over again until eventually he warped close to me enough times to trigger a transition to his third phase. Yes!
The third phase didn't seem to be anything special. I mean, Sephiroth was summoning meteors and flinging them around with his mind which was pretty cool, but I just tanked them all and healed up the damage. Eventually he stopped doing that and started trying to beat me down with his sword and some glowy balls and I was able to work out a pattern where I could just the balls and hit him with a jump attack. It didn't take too much of that to finish him off. I couldn't help myself... I ended up yelling suck it at the screen and went into the DX crotch chop. Oh yeah!
Expert mode Sephiroth dead! I guess I should go finish the game now. There are some other optional challenge bosses but none of those matter nearly as much as Sephiroth. And man, that introduction to the fight... I can remember that happening back when I first played the game and One Winged Angel started up before they announced who the enemy was and I marked out HARD. So good.