Trials of Mana is a long game filled with things to see and enemies to fight in true JRPG fashion. However, even after the game concludes, there are still some bonus fights, one of which is a secret boss called Black Rabite.
As indicated by its name, the Black Rabite takes on the shape of what looks like a black rabbit. The only differences are that it has no feet, its face is larger, and it has highly malicious intentions despite its cuddly appearance.
Defeating this secret Trials of Mana boss will grant you the Rabite Trapper achievement, though finding this boss will take a bit of time.
First, while it is unnecessary to take on any post-game content right away, players will need to finish the game and defeat the game's "final boss." Upon doing so, players will have open access to the game's world once again.
Once given the ability to travel anywhere, players must head back to the area they were in just before going to the last story dungeon. This is dependent on the character chosen in Trials of Mana. As such, for Charlotte or Kevin, players must go back to Mirage Palace. For Angela or Duran, players must revisit Crystal Desert. Finally, for players who choose Hawkeye or Riesz, they must go back to Night Cavern.
Once at one of these locations according to the appropriate character, players will notice a black statue in the shape of the Black Rabite. Interacting with it will give players the option to investigate its "strange aura," sending them to a new area that is inhabited by the Black Rabite.
The area is rather creepy, which is befitting of the deceptive rabbit-like creature that can inflict atrocious amounts of pain on the player.
Defeating the Black Rabite will reward players with the Rabite Trapper achievement, as well as bragging rights for having defeated the über challenging boss. The Black Rabite has been called the toughest bosses in the game, despite its warm appearance. Although, it isn't as if gaming hasn't ever introduced players to a boss whose appearance was deceiving, turning out to be formidable foes later.