Final Fantasy X - Ultima Buster at Low-ish Level, No Mix/Oblivion/Delta Attack

Ultima Buster's not that bad in the grand scheme of things, and with good enough luck I think it would be possible to farm a perfect attack pattern out of him and beat him without using Aeons as sacrifices. This would take a substantially long time, though, and I'm not willing to attempt it. So for this encounter I've dropped the No Aeons restriction so I can use them as damage shields. I still leave a restriction in place to not use the new multi-hit Overdrives added for the International release, so this tactic should work on the original release as well, possibly even better with Rank 1 Quick Hits.

First let's talk about the pros of Ultima Buster. If you take out his arms, his body has virtually zero defense. The arms themselves have pretty high physical defense but still take huge damage from Overdrives. The head is a nuisance, but once killed won't regenerate. All in all this makes Ultima Buster a big pile of meat for you to abuse. If you got past Neslug, chances are good you can get past Ultima Buster, although I strongly suggest a decently leveled Wakka for this fight.

Now the cons. The arms will periodically regenerate, cutting off your offense and requiring you to shift attention back to them. Auron's Dragon Fang is great at handling the arms, but if they respawn at a time when Auron's Overdrive isn't full they can become a problem. If the head is left alive, it essentially functions as a second attack opportunity for Ultima Buster, so you need to kill it immediately before its first turn. The head is an "out of range" enemy with decently high Magic Defense and HP, though, so killing it before its first turn isn't trivial.

If I understand Ultima Buster's AI properly (my confidence is very low), then here's how he works: starting on turn 3, every odd-numbered turn will be Ultima. So on turns 3, 5, 7, etc. he'll cast Ultima at 100%. On every other turn (including turn 1), he has a 50% chance of using Ultima and a 50% chance of attacking. This means it's entirely possible for Ultima Buster to cast Ultima on every turn, and I've recorded him going at least 7 turns in a row with it.

This is why I think it might be possible to do this fight without Aeons, but I'm unwilling to try. You need Ultima Buster's AI to do Attack, Attack, Ultima, Attack, Ultima, Attack... ad nauseum. If he ever casts back-to-back Ultima, you can't really recover with characters having Agility as low as mine.

Instead I use my Aeons as sacrifices on the 100% Ultima turns. Between these turns I try to get Yuna to get Auto-Life up on the entire party, for when one of the coin-toss turns chooses Ultima. I need this to not happen too many times, or I won't be able to keep my offensive output high enough to kill Ultima Buster before I run out of Aeons to use as sacrifices.

This makes Wakka nearly essential, at least with Strength stats around 130. Tidus will do almost a third as much damage with Blitz Ace as Wakka does with Attack Reels, dragging the battle out substantially. Auron could be replaced with Tidus, using Energy Rain to kill the arms and Blitz Ace when other opportunities arise. It's generally more valuable to just Entrust to Wakka, so I stick with Auron for slightly better Quick Hit output.

This fight goes quite well and I manage to kill Ultima Buster after 4 Aeon sacrifices. In theory I have up to 8 total, but the Magus Sisters are too powerful and one of them will survive Ultima, which throws things out of cycle.

This is most likely the end of this video series. On the original release of the game, if I pumped my current 100 spare levels into my characters to build up their Agility specifically, Nemesis is possible by memorizing his AI script (which is partially deterministic) and summoning Aeons as sacrifices. In the International release, the nerf to Quick Hit's recovery time makes this unattainable without much higher levels.

EDIT: I was able to defeat Nemesis (   • Final Fantasy X - Nemesis at Low-ish ...  ) by raising everyone's Agility to 170, so I could have done that before this battle and beaten him without Aeons easily. Ultima Buster's Agility is a measly 72, so Yuna could perform Quick Pockets Mega Phoenix and then Auto-Life herself after every Ultima, trivializing this encounter.