Minotaur

His mind told him, if he entered, he could find something related to the dungeon, like how the dungeon works.

'Forget it, I have no time now, and Olivia's condition is also uncertain.'

Emily was in a daze as nothing changed after the light disappeared; the monster she expected didn't come out.

Seeing her face made Alex chuckle, "Don't worry, I caught the monster. Let's go finish the dungeon."

"You already caught it?" Quartz asked in disbelief while Zold had already turned around, making his way out.

Alex then explained to them the monster he just captured. 

It has a similar type of ability to Emily, capable of controlling and creating light. But the ability is less destructive, and the monster has more control over it.

Alex also thought it was possible the crystal had a special property that reacts to light. Or it's just how the monster uses its ability.