1.) You can learn Ultima with the Paladin shield and Terra learns it naturally at level 99 2.) You can learn the Water Rondo if you have Mog when you go through the Serpent Trench. 3.) Alternatively if you have the GBA version you can also learn Strago's Grand Train from Omea Weapon. Force Field shouldn't even be a Lore because the boss is located in the final dungeon and at that point it's pointless since you're finished everything else in the game at that point. 4.) There are a few items that you can only have one or the other for which is annoying as hell for someone who wants to collect everything but technically you have achieved everything because to get said items required you to have the others. 5.) None of Gau's Rage abilities are unobtainable you just have to be persistent and dedicated and make sure you don't leave any stones unturned. But for somebody who is looking to 100% complete that really shouldn't be an issue. All and all nothing in the game is really unachievable. Lots just need some prior knowledge or dedication. Back when I originally played this back in the 90's I was obsessed with the game and managed to figure out most of the games secrets on my own just through exploration and interacting with most things. Back in the day games had a lot more secrets then they do today and it was pretty common to talk to everyone and interact with almost everything in the game. You probably wouldn't find the Atma Weapon without a guide or back tracking and interacting and then some more exploration.