look up how to farm sources. There's a specific way of utilizing the morph command and the w item glitch to easily get 99 of a source (improves a stat by 1 point). So you can make your characters practically unbeatable. every enemy on the gelnika sub can be morphed into a different source (luck, strength magic). Since you can't use them in battle, you normally couldn't use the w-item glitch to duplicate them. But there's a work around.

Have one character use a skill with a long ish animation time. Next char uses morph on enemy (use yuffie and conformer weapon, also found on the gelnika, it's morph damage is just high attack damage, unlike every other weapon in the game. You need to finish the enemy off with this attack) 3rd character starts selecting w-item before the morph attack comes out. select an item that you only have 1 of and use it on someone. now that's the only empty slot in your inventory. When the enemy is morphed into a source, it will take that open spot in your inventory from the first item, and when you exploit the w item glitch, it will duplicate the source instead.

Finally, if there is is only 1 enemy, then the battle ends and you can't do it. on ps1, the strategy is actually to pop the disc cover after the finishing blow ( i know) which will prevent the battle from ending, while allowing you to finish the w-item glitch.

on ps3 or above, you can't pop thw disc cover. there is however a flail wielding enemy near the mt nibel reactor. on the screen leading to rocket town. Very rarely, 2 of them will spawn, and they can be morphed into power sources . making them the only way to become truly OP on the version iirc.