Shamelessly stealing this idea from Anomalous Subsurface Environment for my Clash of the Titan campaign. This creature was created by Henchmen Abuse so all credit to him. I used this as a support monster in a battle with a medusa who had the entire room mirrored so it was impossible to escape her gaze. When the characters closed their eyes the glass minotaur emerged. I used the sound of scissors to indicate its movement (helpful video) whenever it moved and actually had my players close their eyes. Worked well.
The glass minotaur is exactly what its name describes – a minotaur made entirely of glass. It is completely transparent, with the exception of its translucent red heart and eyes.
Charge. If the minotaur moves at least 10 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 9 (2d8) piercing damage. If the target is a creature, it must succeed on a DC 14 Strength saving throw or be pushed up to 10 feet away and knocked prone.
Reckless. At the start of its turn, the minotaur can gain advantage on all melee weapon attack rolls it makes during that turn, but attack rolls against it have advantage until the start of its next turn.
Silent Antagonist. The minotaur is completely silent except for the sound it makes cutting the air as it moves (similar to the sound of scissors).
Mirror Gate. The minotaur may move freely through mirrors to other reflective surfaces within 10’. It thus prefers to live and fight in mirrored labyrinths.
Glass-Storm. When it is slain, the minotaur’s body explodes into flying shards of broken glass, causing 1d8 points of necrotic damage to all within 10’ of the minotaur. Only its heart and eyes remain intact – the red eyes are worth 50 gp each, and the heart is worth 200 gp.