Labyrinth Minotaur — ruling 1

If the creature Labyrinth Minotaur blocked is untapped at the time its controller’s next untap step begins, this ability has no effect. It won’t apply at some later time when that creature is tapped.

Labyrinth Minotaur — ruling 2

Labyrinth Minotaur doesn’t track the creature’s controller. If the affected creature changes controllers before its old controller’s next untap step, this ability will prevent it from being untapped during its new controller’s next untap step.

Labyrinth Minotaur : règles, fonctionnement et interactions (MTG)

Labyrinth Minotaur is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever this creature blocks a creature, that creature doesn't untap during its controller's next untap step.

How it works : Labyrinth Minotaur

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
If the creature Labyrinth Minotaur blocked is untapped at the time its controller’s next untap step begins, this ability has no effect. It won’t apply at some later time when that creature is tapped.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
Labyrinth Minotaur doesn’t track the creature’s controller. If the affected creature changes controllers before its old controller’s next untap step, this ability will prevent it from being untapped during its new controller’s next untap step.
No other card is named in this ruling.