After taking a week off I came back and finished grinding my HP Up Materia, along with pretty much maxing out all the other Materia I still have left, then retried the Three-Person Team vs. Top Secrets series. For some reason I had a bit more trouble with Shiva than I did the first time, she just kept healing up and would not Stagger despite pelting her with Fire attacks, but she went down eventually. Fat Chocobo was cake again. Leviathan was a bit easier since I knew the fight, I conserved a lot of MP.
I went into Bahamut fully healed and full MP again. I tried every trick in the book I had to try and Pressure and Stagger Bahamut before the first Megaflare. A lot of videos and guides suggested "Just use Counterstance, works really good." I had no such luck either attempt at getting Counterstance to work right. Even if Bahamut attacked while it was up, he was more apt to knock Cloud back than anything. I also tried ramping up Tifa's combos and unleashing them, as that was supposed to be a sure-fire way to pressure him, but had no such luck with that either. At some point I did end up Pressuring him briefly, but I have no idea how it occurred because Bahamut had just knocked Cloud on his ass and Tifa/Barrett either too far away or had no ATB to really build the Pressure. In any case, I ended up SOL come first Megaflare, but before the countdown was over I was able to Manawall two characters and the third had a Reprieve weapon on. All three characters subsequently survived Megaflare this time since I had HP Up Materias to max them out at 9999 HP.
I continued to try and pressure Bahamut in Round 2, but had no luck here either. He immediately started going into his countdown again, and after burning a few Limits just to do some damage to him he hit 50% and summoned Ifrit. This ended up making the fight a lot easier as I had maxed Fire + Elemental Materias in two characers armor slots, so they ended up getting free health back from Ifrit's attacks. I continued to pummel Bahamut as best I could, and when the 2nd Megaflare came up I used Manaward on two characters and Manawall on a 3rd to try and save some MP (Barrett was almost empty at this point from healing). Everyone survived the 2nd Megaflare again, and by this point I had nearly chipped Bahamut's health to 0 just from normal attacks and abilities. Barret got his Limit late and I finished Bahamut off with that. Afterwards there was still Ifrit to deal with, and because two characters were absorbing most of his attacks for free heals I just sat there for about 4 minutes trying to let Barret's MP slowly regain. He only gained about 7 MP before the AI players finished Ifrit off.
Got to Pride and Joy. I heard he was a pushover after Bahamut, and that's no joke. Couldn't believe how pathetic he was. Aside from his one hit kills on characters, which don't happen that often, you can just stand behind him and punch the hell out of him. As long as each character has a Revive Materia you're fine. I didn't even need Barrett to heal this one, I think I dropped two Prayers the entire fight and had to use Arise on Cloud two or three times. When the bot got low I summoned Bahamut so he could get finished off by a Megaflare for laughs. I'm glad to be done with this little achievement. I'm going to finish the rest of Chapter 17, 18, get my remaining manuscripts and put a fork in it. Looking forward to getting away from this buggy combat.