I finished Titan Souls. Took me a while but I finally did it. Clone Soul was surely the hardest boss, which made the last «secret» boss kinda of a cakewalk.
I almost lost the secret boss because I never found the Knight and Mimic boss while roaming, but I know they existed so I just backtracked the game until I found them.
This is usually a common trend on games with open maps, I just can't find things and get lost easily, a reason for me to just avoid the Souls series outside the very 1st one which had less exploration.