Breaking Raiden - how to add a new Esper

PowerPanda said he added an event to acquire a Magicite from the Dirt Dragon fight

Indeed, I did. If you're going with a mostly-vanilla game progression, it fits really nicely here. The Opera House kind of only exists in the WoR for this one boss battle, and the reward for defeating it, the Magus Rod, doesn't seem like enough for going so out of your way to find it. So, it seemed like the best place to drop in an extra Esper. I chose to move Terrato there, and have my Esper, Leviathn, replace Terrato in Umaro's Cave.

If you want to take my route, it can be difficult to actually FIND the scene you need. It's hidden behind several conditional jumps. The scene you need starts at CA/B6D6. Right at the end, there is a pause and a dialouge box that you can put together, and then replace with a subroutine jump.

EDIT: Attached is a Leviathan sprite that is a modified version of the sprite used in FFV, FFVI Advance, FF Record Keeper, and Pictologia Final Fantasy. The tail is ever-so-slightly shortened so that it fits completely within Raiden's sprite mold. Anyone is welcome to use it if they would like.