Three consecutive battles of varying difficulty.
We begin with the Left Fin. This is the type of battle where you must know the AI in order to win. After you move in, he'll use Gravija on the fifth turn. On the first three turns he'll either remain motionless or use his dangerous regular attack that deals ~1400 damage and causes delay. I don't know his AI down to every detail, but he seems to use this attack more frequently if you attack him, so it's best to wait until the third turn. The fourth turn is used to gather energy for Gravija, and Gravija itself is completely harmless. With Supreme Gems, you will defeat him before he can use the regular attack again.
The Right Fin is easier because it never uses this attack on its first three turns if you don't attack, so just wait until the third turn and toss those Supreme Gems.
Sinspawn Genais is dangerous, but he doesn't have much HP. He will oneshot Rikku with Venom, so make sure she's not in the party when he attacks. After one attack, you can take him down easily before he gets another turn. With Genais gone, the Core is activated, but it's completely harmless if you have Reflect.
NSG = No Sphere Grid
NS = No Summons
NC = No Customizing
NRI = No Regular Items
NM = No Mix
![](https://i.ytimg.com/vi/Xppna_JmRCQ/maxresdefault.jpg)