Selphie's limit break in this game is very much like Cait Sith in FFVII. He also have a slot but just kinda different. Her slot are random but you can retry the slot over and over again. Or you can just cast it on your party or on your opponent. The spell in her limit break is not the one she drawn from her enemy. But also not every spell is in her limit break. If you keep retrying her limit break just to get the spell you want, your other party might be KO because while you're retrying to get a unique spell, your enemy can attack, meaning the wait mode is off. Here are a list of her spell
Full Cure - When you get her limit break and got Full Cure, she will restore all her party members' HP to max. Very useful when fighting strong enemy.
Wall - When you are in need of protection, Wall is a great spell to cast. Wall has a effect of Shell and Protect. It is really helpful when your enemy casts spell on you or just attack you with a very strong attack.
Rapture - This spell is really hard to get in her limit break. This spell will send the enemy to orbit by putting wings on their watch them go. Of course this spell won't work on any bosses, but it's good when you're in a hurry to get somewhere or someplace.
The End - A very good spell that is very hard to get. This spell is one of the strongest one Selphie got. First Selphie will take her opponent to a field of flower and put it to sleep. This spell won't work on any undead enemies. The End spell is very hard to get but it will increase the chances when you're on an extremely high level. It also increases when Selphie is almost knock out.