FFX Luck and Fortune spheres "easy and fast"

Keep 2 characters on low stats until the end, just don't develop them. They'll help you farm those spheres super fast later.

Comrade overdrive fills the gauge depending on the damage the ally takes in relation to his/her max HP. So low max HP and low defence stats = full overdrive to Wakka and Tidus on every hit, 100% guaranteed.

Don't use Yojimbo, because Zanmato doesn't do Overkill, which gives double reward.

You can fill everyone else's grids full first, and then fill only luck spheres with those low stat characters (with help of teleport spheres from Sleep Sprout). After you have 255 luck on those low characters, you can go and fill the rest of their grids.

This was done with Expert Sphere Grid, so no, you don't need those extra nodes from Standard Grid to max out all stats. Standard Grid just requires you to do more pointless work to fill the entire grid.

Have fun!

And ignore those typos in the video... :P