Niijima’s Palace is not bad at all, there are often multiple routes that allow you to get to your destination. At one point there is a bodyguard miniboss blocking the path, but you can actually find a way to get around them and even attack the miniboss from behind, please see our video walkthrough below.
You’ll be asked to gamble, but it’s fake. You need to rig the machine to win. For the dice game, you can play a few games, but you don’t have to; rather, look for a vent using L2 and get behind the area.
There’s one section of the level where you need to stumble through darkness. It’s not too bad, just use L2 to find the tricky-to-see vents. If you’re lost, there’s probably a vent tucked away somewhere.
There is an arena fight where you as Joker need to fight multiple waves of miniboss enemies one-on-one. The Thor battle almost reminds me of SMT: Nocturne’s Thor boss fight in an arena! But more seriously, equip a good persona that doesn’t have weaknesses, and it’ll help to have buffs for yourself and debuffs for your enemies.
In the worst case scenario, use a bead to heal yourself and get through the solo battles.
Near the final stretch, you need to hack a big casino machine. To do this, you need to hack small green and red panels that you found earlier in the dungeon. Again, it’s not too bad, you just need to use L2 to look for vents and ledges, see our walkthrough below for the locations.
Niijima herself is not too difficult. You will need to waste a few turns waiting for her to spin a roulette wheel, but when asked say that she’s cheating with a glass panel.
When she reveals her persona and transforms, the wheel will determine what elements she will use and what her weakness is. It doesn’t seem to be an official weakness that knocks her down, but it does seem to do more damage.
For example, she lands on the fire symbol and was using fire attacks, so we used ice attacks, and they did more damage although they didn’t knock her down.