||Dragon Scale (x2)
||Water Gem (x2)
You can find the Octopus in the underwater section of Via Purifico. It is an armored fiend, so you will need Piercing on your weapon in order to deal full damage with a normal attack, which is something you probably won’t have with Tidus, Wakka or Rikku. Despite that, its weakness to Thunder means that Rikku can toss Electro or Lightning Marbles at it to deal some good damage. The Octopus only does normal attacks, but it has a few of them. The first will always cause Slow, unless you have Slowproof. The second has better accuracy than normal, while the third one is a little stronger.