Hello friends this will be my fourth playthrough of this hack over the years and I'm excited to see what the full 2.0 will bring to the table. I am playing on the extreme difficulty which I believe gives me 50% extra experience. I don't know if the difficulties actually change the mechanics of the fights or just change the numbers. I'll do my best to give a brief rundown of how I did the bosses in case anyone is interested.
I believe the first boss against the spider has had it's hp reduced from previous versions, which I appreciate. The fight with the esper is a lot more fun and I am afraid this fight might intimidate new players after they scan it and see a really high number of hp. Don't fret though I don't believe you actually have to deal that much damage to end the battle. It's vulnerable to poison, but will cast rippler occasionally to transfer the poison to you, your magitek heal will remove the poison as well as recovering hp so you don't need to use items here. After you've poisoned it for the third time it will use an ability where it cures it's self of poison and does a large amount of magic damage to the party, this nearly killed me, but I healed up Aurora, and revived my other party members. Keep your party in the back row at all times and keep up magitek barrier, let the poison do most of the damage and you will eventually trigger the cutscene.
Be sure to buy some karma jolts at the castle, and arrange your party members the opposite row as normal since the next fight will be a back attack. You're against 2 guys in magitek armor, and once one dies the other gets huge buffs so you want to try to kill them as close together as possible. My tactic was to repeatedly use Serin's tools to confuse them, which will make them attack each other. Once one breaks the confusion hit the other with Cloud to keep the damage even and repeat. Use Aurora to heal and cast spark on both or one whichever is best to keep their health even. In the cave I ran from the battles and you have to fight a zombie at the end. It's not hard but keep in mind that it can zombify your party members, so it's best to keep a few extra karma jolts.