The Tartar Sauce is a pet-summoning item that spawns a Mini Minotaur to follow the player around. It is dropped from Iron and Mythril Crates with an approximative chance of 4.8*6/125 (4.8%). The pet's yellow eyes glow in the dark, but it produces no other light. When the player gets too far away from it, it will twirl its axe and fly to them.
The Tartar Sauce is a reference to the "Mini Minotaur song" by YouTuber Tobuscus. In the song, it is said that mini minotaurs hate tartar sauce and are allergic to it. The buff tooltip, "How do you defeat a mini Minotaur?", is a direct quote from the song.
The Mini Minotaur's appearance, the red loincloth and the hammer, is probably a reference to the Maulotaur from the 1994 dark fantasy first-person shooter video game Heretic and its sequel Hexen, where the Maulotaur can be summoned by the player to aid them in combat.
In the 3DS version, the buff name is displayed as "BUFFNAME (136)" instead of "Mini Minotaur". Similarly, the buff tooltip is displayed as "BUFFTIP(136)".
In Greek mythology, the Minotaur is a mythical creature with the head and tail of a bull and the body of a man. He dwelt at the center of the Labyrinth, and was eventually killed by the Athenian hero Theseus.
In Greek mythology, Tartarus was the Abyss from which many monsters emerged. While the tartar in both of the names may be a coincidence, it could be a reference.