Abilities and Powers
As one of the Demon Guards of Impel Down under Sadi-chan, Minotaurus is in charge of torturing and maintaining various prisoners.
While he does not look like a powerful opponent, Minotaurus is in reality a fearsome beast. He has immense physical strength and speed, along with excellent resilience.
He wields a spiked club as a weapon in conjunction with his strength and speed.
He has eaten an as-of-yet unnamed Zoan type Devil Fruit that allows him to become a cow. Because he is an "Awakened Zoan", he is able to recover rapidly even after suffering high amounts of damage.
Impel Down Arc
It is first seen beating two prisoners up for fighting and locking them up in a cell for death row, then again beating Jinbe in Level 6. Although only its shadow is shown during those times, it is clear that it is a Minotaur that shows no fear. (though at the time, Jinbe was chained down and Jinbe also states that it did not hurt him).
Later as Luffy reaches the Starvation Hell of Impel Down, it gets the order to battle him as well as Bentham, who was supporting Luffy. However, as soon as it sent Bentham flying with a single hit, Luffy recognized its true powers and immediately activated Gear Second and used his Jet Bazooka to send Minotaurus flying to save Bentham.
Although Luffy used one of his powerful techniques to defeat Minotaurus, it appeared later, hunting Buggy and Galdino (it landed on top of them when Luffy sent it flying). At one point they come to meet Luffy and Bentham. Buggy used his secret weapon, the Muggy Ball, to take Minotaurus down, but even after a huge explosion it was still conscious. Even when Bentham used a strong kick to finish it off, it stood still but was in great pain. Only as Luffy and Galdino combined their abilities to use the Gomu Gomu no Tonkachi Rifle, they could fully defeat Minotaurus. He was last seen falling from Level 3.
Later, he fully recovered (albeit bandaged) and joined the battle against the rioting prisoners. Despite all of this, he was defeated (as well as receiving his comeuppance for beating Jinbe earlier) with the rest of the Demon Guards by Monkey D. Luffy, Crocodile and Jinbe in Level 1.
Two Years Later
After the timeskip, Minotaurus is seen with the other Demon Guards with their new member: Minochihuahua.