- Alias: Phantom Knight, The Hollowed, Ghostly Onyx Knight, The Lost Boss
The Lost, also known as The Lost Boss, can be encountered by the players after entering the Hidden Key door in The Grand Hall. Upon entering the door, the user will be taken to The Lost, a small battleground with multiple torches and a wall at the end of the room, enabling players to leave The Lost.
After killing The Lost, the players can acquire the Light Marble upon its death. In addition, a treasure chest will appear near the exit of The Lost, rewarding the players with a random item that can be obtained in the Nightmare and/or the Frontier. More information can be seen in the article, Guttermouth Rewards.
There are six attacks that The Lost can perform:
- Jab - Jabs the players with its rapier.
- Slash - Slashes the players with its rapier.
- Summon Phantoms -The Lost will summon two Phantoms into the battleground. If a clone is defeated, The Lost will quickly summon another for assistance within a certain time interval.
- Teleporting Spin - The Lost will spin around in a circular manner before teleporting to the player's current location, slowing them down temporarily and leaving them vulnerable to the attack immediately performed afterward (which can rarely be a second Teleporting Spin).
- Threefold Advance - Similar to the Great Scimitar's special ability, The Lost will perform a continuous melee technique where the rapier will go in three different directions as the boss swings its rapier around.
- Ultra Charge - Similar to the Ultrablade's special ability, The Lost will charge towards the players with its rapier in an attempt to hit them as it continues to follow the player's footsteps.
While it is possible to attack The Lost from elevated spots or get it stuck on the torches, it is relatively easy to deal with face-to-face, as The Lost and its minions are slower than a Corrupted Onyx Knight in their attacks and movement. With enough walkspeed, they can be easily outpaced and attacked from any range, and the player has more time to jump out of the way of any incoming attacks.
It is important to keep a close eye on The Lost's minions at all times, as they can catch the player unaware and possibly leave them at a low enough health for the boss to finish off. The minions can easily be dealt with using any weapon, as they always take four hits to kill.
- Whenever The Lost attacks, it will make low-pitched sounds of a Dark Ghost's laugh.
- During the development of the Ratboy's Nightmare Update, its placeholder name was titled 'PhantomKnight.'