Mr. 58, also known as the Soul of the Frontier, is the final boss of the Otherworld Tower dungeon, a 50-floor dungeon where players will fight against mobs after mobs on each floor. It is the hardest boss in the Frontier as of the Otherworld Update and is currently known to have one of the highest health pools and attack damages out of any mobs in the game.
In appearance, Mr.58 is a very bizarre-looking creature symbolizing various elements in Fantastic Frontier. Its main demonic-like body symbolizes the various monsters that roam in the Frontier, and possibly any other places within the Frontier's universe. Its three heads below the main body symbolize the three damage types weapons have. The three heads of Mr.58 are also the main colors of Fantastic Frontier, red, blue, and yellow. All of these colors are common in the Frontier as the players begin their adventures.
The first head to the left is seen wielding a sword and is red in color with an eyeball near the top of its head. This particular head represents the melee class. The second head in the middle is blue with a mustache and a chimney-like hat with yellow neon diamonds, but can also be seen as a variant of the Fantastic Top Hat. This particular head represents the magic class.
The third head to the right is yellow with two eyes at the end of its 'stalks' coming out of its torso. It also has wings on its head. It is noted that it also has a massive gun extension from its body. This particular head represents the ranged class.
Mr.58, also known as the Soul of the Frontier, has the most attacks in the Frontier as of the Otherworld Update. In addition, each head has three attacks whilst the main head has one. It is recommended to have one of the many best armor sets, as well as having at least 600 HP to avoid the risk of getting one-shotted by Mr.58's attacks.
- 3 continuous attacks from left, right, and middle.
- Heavy-damage attack close to the left side of the Magic Head.
- Normal attack close to the left stage sliding across towards the Magic Head.
- A massive laser is cast down onto the middle lane. Players should be aware of the fact that its hitbox is so huge, that it fills the angle of the middle hexagon.
- Spray-like shots are cast from the right, then to the left, then to the right, then to the left. A four-time continuous attack.
- Ice shards appearing out of the ground in order to impale the player(s).
- A rapid-ranged attack from the right lane to the middle stage.
- The ranged head stands still and shoots a multitude of bullets.
- 2 gigantic bullets are summoned, one bullet traveling near the main body and one bullet traveling outside of the main body. The main body is the first and bullets can curve from the outside to the inside.
- A gigantic laser is cast from the left stage all the way to the right. An echo-like laugh occurs before this attack is cast.
- Mr. 58 is the final boss of the tower, defeating him for the first time rewards the survivor with The Pommel's Helmet.
- Hitting multiple of Mr. 58's heads with a single piercing weapon's attack will only count the first time the individual attack connects because all the heads share a single hitbox.
- Mr. 58's name may have come from the number 58 being associated with misfortune.