I'm currently stuck on the fight against Yukari and Mitsuru. Out of nowhere they suddenly learn Megidolaon and use it back-to-back. I just need to have enough HP to survive two consecutive casts so I can spam Mediarahan while Metis does the damage.

Now THAT was an ending. So much more closure and made a lot more sense than the ending to The Journey. I was worried that Aigis was going to die initially, at which point I thought "Well, that spoils what's going to happen to the main character in Persona 4" but I was very pleased to see her come out alive. Minato wasn't revived, but at least they explained why he died.

the 4 final bosses were not really difficult, but they are rather tricky. I think I was beaten like 15 times or more before I could figure out the most optimal strategy
Akihiko and Ken = Kill Ken first, use tetrakarn to force them using magic
Koromaru and Junpei = Kill Junpei first, use fire break if you want to use Ragnarok (Surt ultimate attack), use siegfried since it could null slash.
Yukari and Mitsuru = Kill Mitsuru first, equip eye of wind or anything to null wind attack. Your best persona is Yorlungur with mediarahan, whatever you do, don't use Makarakarn because in next turn they will use megidolaon.
Erebus = Keep your hp always at maximum, use mind charge at the beginning of turn so you could use your most powerful magic when he using Dark Embrace, after he's down, cast any supportive magic to your party members

My level is 77 btw, and they are not really difficult, but pretty much tricky