The final boss(es) of Shin Megami Tensei IV. Either of them. Not because they’re hard, but because when you get to them they’re overwhelmingly pitiful.
SMT IV is a game I like a lot, especially aesthetically, but it has some truly baffling gameplay choices. One of these is that the difficult is very top heavy. The intro area and first two bosses can be colossal pains in the ass, and after that things are MUCH more manageable. You’ll occasionally have a difficult boss fight, but nothing as bad as those first two.
Then you get to the final bosses, and they just don’t have anything to challenge you. You’re heavily stocked with tools that easily grind them down, and while the bosses have unique moves, none of them are likely to be that dangerous to you. They’re opponents that should be grueling to fight, but chances are you curb stomp them.