How do you defeat spherimorph on final fantasy x?

Answer 1

The Spherimorph is one of the more complicated and unique bosses in the game, but once you know the trick it can be really easy to defeat.

You'll want Lulu in your party at least, as elemental magic is the most effective against this boss. (if you chose to put Kimahri through Lulu's portion of the Sphere Grid, he'd also be effective here)

Spherimorph changes its elemental affinity every time it is attacked with elemental magic. Unfortunately, the game won't tell you specifically which element it changes to.

Of course, this is where the trick comes in. See, Spherimorph will cast the spell of the element that it is. For example, when Spherimorph has changed to the Fire Element, it will cast Fire on your party. Therefore, what you want to do is wait for Spherimorph to tell you which element it is by attacking your group, then using Lulu to cast the opposite element. Remember that Thunder and Water are opposed, and so are Fire and Blizzard.

One thing that I found useful in this battle as well was to Haste Lulu with Tidus.