Sinspawn Gui Sinspawn Gui is the result of the Sinspawn gathered for Operation Mi ' ihen fusing into a monster that breaks out of its cage and fights the party in " Final Fantasy X " , just as Sin approaches the shore . The party is scattered by Sin ' s attack , and Seymour Guado grapples with the reanimated body of Sinspawn Gui alone until he is joined by Yuna and Auron ; both encounters count as one boss . Battle . Sinspawn Gui is made up of four parts : the body , the head , and two arms . The body and the head act independently . The arms do not act , but will regenerate after the body gets either three or four turns with both arms dead . The head , in both battles , follows a set pattern . It will use Thunder , and on its next turn start " moving suspiciously " , followed by using Venom on the turn after that ( which causes it to stop moving ) . It then repeats this pattern . If the head is attacked between when it starts moving and when it uses Venom , it will stop moving , and will not use Venom , but will restart the pattern starting from Thunder on its next turn . The arms do not attack , but they shield the body from physical attacks . When shielding , the arms count as Sinspawn Gui having 100 defense , regardless of whether there is one or two of them present . They do not protect the head . First Battle . The body follows a pattern of alternating between physical attacks and Demi . There are some special cases , however . On its first turn in the first battle Sinspawn Gui will use a physical attack , but this does not count as part of the alternation ; it will begin the alternation ( starting with another physical attack ) from the second turn . It may skip the physical attack and go straight to using Demi when the head is dead and the body is below 4 , 000 HP . Though the first form gives no spoils immediately , Overkill still matters as item drops will be rewarded after the second battle . The rapidly proliferating potential supply of Lv . 1 Key Spheres at this point makes it possible for Steal to be accessible on the Sphere Grid , but stealing from Sinspawn Gui will yield only Potions . Strategy . A few party member Overdrives and both aeon Overdrives will see good use here against all four available targets simultaneously . Tidus casting Haste on himself and then other party members will maximize the ratio between party actions and those of Sinspawn Gui . Auron ' s and Kimahri ' s attacks are effective against the armored arms , and killing them enables further physical attacks against the body . The arms will regenerate , but count as separate enemies for the purposes of awarding AP ; each kill will add its AP to the total . Once the head begins moving ( if the player has not already killed it ) , Wakka , and Lulu will be alerted . If left alone , the head will use Venom on a character , but Lulu ' s spells , Wakka ' s attacks , or Lancet will cancel the poison attack , or the Poison can be negated by Esuna for the same action as cancelling the attack , which frees up magic attacks for killing the body . Second tier spells , such as Fira , should be strong enough to kill the arms in one shot , or can be used on the body to bypass the arms or eliminate the head and its poison threat . Second Battle . Only Yuna , Auron , and Seymour Guado will be available . Seymour is equipped with the second - level Black Magic spells ; he is much more powerful than Lulu or Yuna and can easily defeat the monster on his own . Waiting for Seymour ' s Requiem Overdrive to charge will take some time , but this is the only opportunity to see it . Sinspawn Gui does not have an extra attack at the start ; it begins the alternation from its first turn . After a certain point the body is not guaranteed to use a physical attack ; it may skip that step and go straight to the next Demi . This happens as soon as the body has taken any damage , even if the head is still alive . Strategy . The most common strategy is to have Yuna keep the party healthy while Auron and Seymour attack . Seymour has Sensor , and thus the player can ensure he gets the killing blow with a tier 2 Black Magic . This will Overkill Sinspawn Gui and double the number of Lv . 1 Key Spheres awarded ; six rather than three .