Romancing SaGa 2 (HP)

This achievement is earned early in the game (second bloodline).

Travel to Nibel (in South Varannes) and speak with people around town. The old man walking around outside will mention "Brawlers train at the Dragon Lair in the Western Mountain." With this knowledge, travel to the dragon lair and follow the one path down stairs and to the end. Speak with the Brawler character and he will ask you to take care of some slimes, but that they will kill the other boss.

Leave the Dragon Lair and travel to Fiends' Cloister. On the second floor, there will be a stationary slime blocking the door. This is the enemy you need to kill. It has around 800 health and regenerates 80 life per round. Magic spells will deal a lot of damage to it, and I also found that a high level sword skill (11-12) using something like smash, or mince dealt heavy damage. Make sure your formation is set to free for all, so its lightning attack only hits one person at a time. Definitely save before the fight, because it can be a tough one.

Once you dispatch the slime, head back to the Dragon Lair (while you can go into the next room, it's not necessary. IF YOU KILL THE BOSS IN THAT ROOM, THE BRAWLER WILL NOT JOIN YOU, but it appears you can still unlock the achievement this way) and let the Brawler know of your victory. Head back to Fiends' Cloister and now go into the room the slime was blocking. All the way in the back, the brawler will have an enemy surrounded. Talk to the Brawler, he will kill the boss, and thank you.

Now you can recruit the Brawler from the Dragon's Lair