~Deal 99999 damage with one attack~

This trophy can take a while to earn as you will need a weapon with Break Damage Limit. I would recommend using a character's Celestial Weapon as on top of having Break Damage Limit, they have other criteria that assists the character doing more damage; Tidus, Wakka, Kimahri, and Rikku's weapon do more damage the closer to your Max HP you are. Auron's does more the further away from his Max HP is. Lulu and Yuna do more the closer to their Max MP they are. If you're not using the Yojimbo method in the end game this trophy should come naturally as you work to max out your stats.

If you are using Yojimbo and not maxing your stats, you'll need to work a bit to earn this trophy. Keep in mind you can also get a Critical Hit with a physical attack or use an Elemental Weakness with a magical attack. Some Overdrives also do a single hit for more damage and you can use those to also raise the damage potential. You should also be attacking an enemy with a very low defense/magic defense stat and if not the enemy should be susceptible to Armor Break or Mental Break to cancel out their defenses. There are many ways to reach that damage potential but nothing is better than having a high or maxed out strength/magic stat. You'll earn this trophy once you hit an enemy for 99999 in a single hit.