Local Enemy Bestiary
When you return to controlling Tidus, you’ll have a pretty clear path to go along for a while. On the way, you’ll meet up with Auron - he will ally you for a while, and he can be quite the physical powerhouse. In any case, continue along the path outside of the stadium. After a strange scene with the hooded child, continue along the path to Auron again. This scene will culminate in a battle with Sinscales - consider them the Goblins of other Final Fantasies: weak and they love death (we assume). You’ll also get the Longsword weapon from Auron during that battle, which teaches you the basics of FFX battle.
Continue along through the groups of Sinscales. As you do, you’ll end up getting surrounded by them. While you could grind against them in normal RPGs (indeed, I did the same thing when I was younger and rash), they yield nothing, so don’t bother - attack the ones directly blocking you and move on. Don’t worry, they’re too weak to cause legitimate damage. Eventually, you’ll encounter something a bit … bigger.
BOSS - Sinspawn Ammes
You’ve already dealt with the Sinscales thus far in the main game (and more than enough, I might add - they’re annoying, eh?), so you should be familiar with their simplistic offense. Sinspawn Ammes is different: it relies ENTIRELY on Demi. Demi is in fact its weakness in this game: it eliminates 25% of the target’s current HP. That seems like a huge problem, but worry not.
This battle opens up with Auron having his Overdrive as well. Overdrives are like the specialest of attacks in this game. These attacks typically deal higher damage than normal, sometimes deal additional effects, and often can also hit multiple times so you can worry less about the 9,999-damage cap. In any case, Auron’s Dragon Fang requires you to press a simple sequence of buttons to induce an attack on all enemies, which, if executed uncrappily, should kill all of the Sinscales.
And what does that mean? There’s only Sinspawn Ammes left! And what does that mean? You’ll only have to deal with Demi! And what does that mean? You can’t die! … No, seriously, you won’t. Since it shaves off 25% of your current HP, the most it take is 1 HP (2~4 HP), and it rounds down for the damage, so at 1 HP, you take (0.25*1 = 0.25, floored = 0) damage. So, put them Potions away: eliminate any Sinscales that you somehow didn’t kill - throws Vita at you - and then Attack the crap out of Ammes.
Though what happens if it hits zero MP is beyond me. As far as is known, Demi is supposed to account for 32 MP in consumption, enough for 12 Demi castings. However, it’s been noted that the boss does quite a few more than that, with no end known. Perhaps the boss is using a special variation of Demi specifically drawn up for it that costs very little MP (i.e. zero)? Whatever the case, don’t expect it to actually run out as far as is known.
After the fight, continue along the highway overpass to the Save Sphere. Yay! Examining one fully heals your party’s HP/MP/status (and your HP probably took a beating) as well as lets you save the game. Continue along again to a battle with some Sinscales and continue fighting them off. Eventually, Auron will suggest to attack the generator nearby. Attack it a few times without regard for the Sinscales to … well… In any case, a scene occurs and you end up floating elsewhere during it. During that part, just press Circle to go down to continue the scene.
You’ll later end up somewhere … else.