Personally Mother Trinity takes the hardest boss title in my book. She was the first boss in the entire game to truly make me die (I have a HUcast so they have enough HP to survive most things). Actually I may have put that wrong. I did beat Mother Trinity on the first try but she made me waste my three scape dolls and nearly all my healing items. Moments later I was thrown into a battle with Dark Falz who took an easy win. I was quite unprepared against her weapon wise too. I was fighting with Scarred Horn+16, which is a spear type weapon. So I was having to do close range combat to damage her.
Her first phase when you just have to kill two of the three Mother Bits floating around was easy I just had to stay on the correct titles to avoid an electric shock. But her second phase without even worrying about the consequences I ran up and started attacking her. Worst thing I have ever done in the whole game. She then face planted herself on top of my whole party killing everyone and leaving me in critical health
. I never had any long range weapons with me so I had to time my attacks and get out of there if I felt she was gonna squash me again. Also those damn homing beams she shoots out. That’s nasty fortunately if you time it absolutely perfect you can roll out of the way to save yourself. Anyway it was a miracle I managed to beat her but Dark Falz destroyed the moment
. On my second go I was smart enough to bring with me JellDeo Twins+35, which is two Mech Guns. This allowed me to keep my distance for both her and Dark Falz. 
Long story short Mother Trinity was an eye opener and I’m kind of glad she put me through hell, a good boss in my opinion makes you use your head and re-think strategies.
