The minotaurs immediately noticed it. How wouldn't they, when they were completely devoted to their duty, unlike grolls? With increasing fear in their hearts, they looked as the light began disappearing, first from the start of the path and then from the whole cave. A dark cloud was quickly approaching them like a wave of darkness, and soon it swallowed them, leaving them completely blind in its night. Yes, minotaurs couldn't see in the dark, and they were afraid of whoever did this (for they, of course, knew that somebody was responsible for this), but they didn't even think about running away, and they stubbornly waited for a fight. The moment of their purpose has come. Someone was obviously trying to get past them, and they would do anything in their power to stop him. Some of them even tried lighting torches, but as soon as the flame appeared, it instantly disappeared, extinguished by a powerful, unseen force. These failures made them give up on the idea.
Then suddenly, a sound came from the path leading to the fortress. Someone was approaching the gates! Without almost any hesitation, two of the bravest minotaurs jumped down from the wall on the path itself and rushed across the whole distance of the path with their heads bowed down to impale the attacker or the attackers on their horns. They successfully made it to the beginning of the path without any trouble. There was nobody in their way. They were confused, and then, after a few seconds of lightning-fast movements and bellows of pain, they were dead.
Their comrades heard their demise from the walls and became even more stricken with fear. There wasn't an enemy in all of Elysium a minotaur would be scared of fighting, not even if it was the mightiest Hell Purger of legends! They were that brave and reckless. But this was something else. Angels never fought in the dark; they were creatures of the light. These were the methods of evil, and that meant that a demon was attacking, which made no sense. Why was one of their own attacking them? Confusion and fear started spreading through the ranks of minotaurs who genuinely didn't know how to react to this situation they were so suddenly thrust into.
A sound of something heavy entering water could have been heard from their right! Nobody did anything. After about ten seconds, another such sound was heard from their left! Still, nobody had the bravery to do anything. Then a series of smaller and quieter sounds could have been heard from both sides, like something was hitting the surface of the water. It was the enemy moving closer to them to siege them, surround them, scale their walls, and kill them all while they helplessly stood dumbfounded! They could not let that be! They were minotaurs; they were mighty and fearless, and they lived to die in the battle, and they would rather kill themselves than be brought to shame like this!
Filled with bravery, despair, and resoluteness, all of the minotaurs started to jump down from the walls. Some jumped down into the water and others on the path itself, charging at their enemy. One by one, minotaurs started getting killed by their unseen assailants. They knew that much because their brethren were letting out bellows of pain from one side, and they rushed to that side blindly to help them. But then the cries of pain could be heard from the other side of the cave entirely, and they would rush there.
Chaos and mindlessness ensued in the ranks of the minotaurs. Spraying of the water was indiscernible from spraying of the blood, friend from an enemy and enemy from a friend! They began swinging with their weapons wildly in the direction from which the bellows of their dying ones were coming. The swings of their sharp axes, spiky metallic gloves, big hammers, and maces all began connecting with bodies of supposed enemies but instead resulted in bellows of their brethren! Brought to the brink of madness by fear and rage, which they couldn't aim at anybody other than themselves, they started killing each other.
The noise, that hellish noise! It was awful. It was like somebody was slaughtering dozens of head of cattle in the most slow and painful way, prolonging their agony unnecessarily. The swiftness with which the minotaurs wanted to surprise and overwhelm their enemy was their doom, and there was no hope of restoring order among their ranks anymore. This chaotic battle in the darkness of the cave continued for a few minutes until suddenly the light didn't return, like somebody decided to turn it back on, and the minotaurs could now see the battle, which, in their fear and confusion, they thought they were fighting for what it truly was. A massacre. A massacre of them, by them and by their invisible enemy, of whom there was no trace.
There wasn't a single minotaur that wasn't dead, dying, or mortally wounded. The water was filled with their bodies that lifelessly floated and were coloured by their dark demonic blood. The air was filled with bellows of pain, and it stank of blood, sweat, and defeat. Those who were still clinging to life shook with fear, waiting for their agony to finally end, terrified by the possibility that the darkness and enemy within it could return. They were obliterated.
This decisive and horrific victory over the minotaurs was the result of Lucius adapting to the circumstances. He was at first completely focused on thinking of a way to make the minotaurs unable to see him, but to keep the vision for himself. This wasn't possible. The sword drew all the nearby light sources to itself, capturing them until he released the pressed gem. It was simply impossible to do it like that so he could see and they couldn't (Lucius kept in mind the possibility that minotaurs could see him in both situations if they could see in the dark, but he just had to take that risk). That was when Lucius realised that he doesn't have to see the minotaurs at all. He could sense them!
While he was still concealing his presence from the moment Old Nigel told him to do so in the dungeon, the minotaurs were not doing anything alike. He quickly realised that, even with his closed eyes, he could pinpoint their exact position just by sensing their presence. That was the advantage he was looking for! He then just had to bait the minotaurs from the fortress, where they were untouchable to him, and he knew just how to do it. First, he extinguished all the light in the cave with the help of the black sword. The sword was even more efficient than he thought it would be, and the whole cave was completely dark in around ten seconds.
With the cave covered in the veil of darkness, he grabbed a few pebbles from the cave's ground and threw them on the path. The minotaurs immediately swallowed the bait, and two of them rushed at him. For a moment, this made Lucius think that this whole attempt at making the minotaurs blind was pointless because it looked like they could clearly see him by the way they were so confidently rushing at him. When he moved out of their way and realised that they did not adjust their direction, he understood that they couldn't see in the darkness any better than he did. With a few quick and deadly strikes, he killed the two minotaurs just as quickly as he would while being able to see.
The demise of their comrades scared the rest of the minotaurs, and Lucius had to draw them out somehow. He decided to simulate a big attack on the fortress as best as he could. He took the weapons of the two minotaurs he killed and threw them into the water on opposite sides. He then started picking up pebbles and rocks, throwing them in the water to make it seem somebody or something was moving in the water and approaching the fortress.
It was a complete bluff. The minotaurs could have simply stayed in the fortress. But the fear and sheer paranoia of being attacked by something you cannot see hurt their pride, and they decided to fight their invaders, not even dreaming that there was only one. Now came the tricky part. Even though he knew where the minotaurs are, Lucius still couldn't see anything else. This meant that he could have easily slipped or tripped over and hurt himself really badly at any point of this part of the plan. Luckily, he didn't. He also realised two very useful things. The water was both shallow and safe, since the minotaurs themselves started jumping in it.
The rest was surprisingly easy. He simply evaded all the minotaurs and eliminated a few of them, which caused panic and chaos, which resulted in them fighting among themselves. He would periodically join the fight to take down a minotaur or two to keep the fire of mindlessness burning, and soon, the minotaurs basically took care of themselves. He then went to the other side and returned the light to the cave. The minotaurs were decimated, and the stairs leading downward were on the other side, just as he expected.
Since the back of the fortress was open, in a sense that it wasn't walled of or protected by a gate but instead had stairs leading into the fortress, he entered it and hoped to find a torch and a way to light it. Quickly he found both a torch and a tinderbox. With a burning torch and a sword in his hands, he continued his descent, leaving the bloody mess that was his victory behind him. Who would tell? Sometimes the simplest approach really is the best.