Oh wow, so it turns out that everyone who was crying about Playful Darkness being impossible to hit was just a little bitch. Who would have thought?
The encounter is absurdly overtuned, but so are your characters by that point. If you throw all your resources at him, you can easily reach the threshold where the only way to miss him is a natural 1. By that point, you have to try really hard not to be capable of stacking a total of +63 to hit (between actual to-hit bonuses and AC penalties).
Such a brutal fight is still unwarranted, though. It should be announced in a clearer way. Not "pop-up that tells you to prepare for the next fight" levels of clearness, but something close to that. In its current state, I don't see how you could ever survive without having failed the encounter at least once. But, again, I can't even see how you could find him impossible to hit after having failed it at least once.