Etrian Odyssey 4: Baboon King (5 Imperials)

This boss is kind of infamous, namely because the quest tied to him shows up a lot earlier than the point where the devs actually expect you to fight him. If you're wondering what that point is, the Baboon King is level 41, so a bit below there. Though some parties are capable of dealing with that quest the moment it shows up.

As for the Baboon King himself, he doesn't do a lot, but he hits hard and always hits multiple people at once. Once you get him down to 70% HP, that's where the fight can start going south if you're not properly prepared for the boss. He'll summon Healing Roller and proceed to spam the hell out of his special attack, Healing Strike. Which hits your entire party very hard and heals him for the total amount of damage he dealt, which can be a giant setback. Crowd control is the name of the game here, as you'll want to take out the rollers fast. Though be warned he also loves to spam resummoning the rollers. That being said if your party has enough DPS to kill the rollers in 1 turn, you'll pretty much see the thing waste so many turns trying to get them back up.

Oh and unlike several other bosses with minions in this game, Baboon King does not have the flag to instantly end the battle once it dies. So you will have to play cleanup if any Healing Rollers are left.

This boss can be cheesed hard though. The reason for this is because EVERY SINGLE ONE OF HIS ATTACKS DEALS BASH DAMAGE! If you're willing to farm for Mystery Shards from the Proto-bots in Echoing Library, you can outfit your entire team with Bash Charms, halving the damage of his entire skillset, making the fight much easier. And laugh at how the Baboon King is a lot less effective at dealing with your party.