this is TOO HARD!!!

[Masamune·1600]

A generalized Nemesis strategy:

-Yuna should be in the party.
-All three characters should have very very high strength and agility.
-Be able to cast Hastega and probably Auto-Life.
-All three characters should have Quick Hit.
-All three characters should have fully powered Celestial Weapons equipped.

If you want to Break HP Limit and/or power up other stats, it's recommended but not totally necessary.

-The Battle Begins-
I usually begin the battle with Auron, since Masamune has First Strike. Unlike Yuna, however, Auron is not requisite. Use who you like. In any case, begin by casting Hastega. The more (quick) hits you can get between Nemesis' turns, the better. Once this occurs, I also give everyone Auto-Life. Depending on your stats, you may or may not want to do this. Anyway, once the characters are imbued with Auto-Life (which may cover more than one pattern sequence, which will be addressed next), you should basically move into a set pattern.

-The pattern-
Attack with Quick Hit. Use nothing else, except (once in a while) Mug, if you're confident in your ability to take Nemesis down. For the purposes of beating it the first time, just use Quick Hit. This will allow you to deal the maximum number of hits between summoning sequences. Ideally, Quick Hits should be hitting for 99999 damage each time.

-Aeons as a break in the battle-
Use Quick Hit until you reach the point where Yuna will be unable to take further action until Nemesis has attacked. On this, Yuna's 'final' turn, call an Aeon. You can do this in any order; I generally start with the Magus Sisters and work my way down. Do what you can with the Aeon (here, the Magus Sisters). It's nice if you can get a Passado or two, but not necessary to the strategy. The Sisters will deal damage; how much they inflict can vary greatly. Eventually, Nemesis should defeat them.

-The pattern continues-
Continue to use Quick Hit; add Auto-Life if you haven't gotten everyone yet. The Quick Hit sequence again continues until Yuna's final turn, where she should again call on Aeon. You may want to skip calling Yojimbo; if he's knocked out in battle, it reduces Zanmato compatibility. If you don't really care about that, he can add an additional 1/8 to the sequence. Anyway, call another Aeon, and have it battle until it's defeated. Again, use Quick Hit with the characters until Yuna's last turn; summon again. Continue this sequence until out of Aeons or Aeons save Yojimbo.

Nemesis may be defeated by this point, if you're lucky. Maybe not. Once the Aeons are gone, however, they can no longer be used for cover. Just keep using Quick Hit. If Nemesis finally gets to attack the party, defensive statistics become more important. If your characters lose all their HP, the Auto-Life castings will bring them back. However, you will lose the Haste, and so not get in as many Quick Hits for the next round. If you eventually get to the point where your party can be wiped out for good (i.e. no Auto-Life, with the possibility of an Ultra Spark or an Armageddon on the way), then Quick Hit until everyone's final turn and then unleash Overdrives. Nemesis should fall at some point during this overall sequence; if not, consider raising your stats further and try again.

There are other ways to beat Nemesis, of course, but this should be effective.

Zanmato can kill Nemesis, but it is not easy to get him to do so in the North American edition. There is information on the Internet that explains how to use Zanmato on almost anything, if you want to follow that path.

Penance and the Dark Aeons are only found in the PAL version of FFX. There are certain other differences, like the lack of an inclusion of Full Break. Essentially, the Dark Aeons are optional bosses which are very powerful. Dark Anima, for example, has 8 million HP, which is far more than any Original Creation other than Nemesis (who has 10 million). They are not, I think it is worth mentioning, the Aeons that Yu Yevon possesses inside Sin. The Dark Aeons are a good challenge, but like Nemesis, are easily beaten with proper strategy. The Dark Aeon quest concludes by fighting Penance. Penance is more powerful than Nemesis, and has 12 million HP combined between its first and second stages.