"Success!" Mu Yang shouted excitedly, but then he began to stagger due to the injury on his arm and the exhaustion of his physical strength. Mo Xi and Mu Li hurried forward to support him.

"Uncle, how are you?" Mu Li asked with concern.

"I... I'm fine, my arm is just a little numb." Mu Yang forced a smile.

Mo Xi checked Mu Yang's injuries and said, "Fortunately, it's just a superficial wound. He just needs to recuperate after returning. Now we have to quickly figure out how to use this treasure and stop them from destroying the Yin-Yang Realm's next plan."

The three of them carefully observed the treasure in their hands. The treasure was shaped like a key and was engraved with mysterious runes all over. The runes flickered with faint light and seemed to resonate with the surrounding space.

"This looks like a key. Could it be used to open something?" Mu Li guessed.

At this moment, they suddenly heard heavy footsteps coming from the depths of the passage. The sound was getting closer and closer, accompanied by a powerful and evil breath.

"Oh no! A powerful enemy is coming," Mo Xi said alertly, quickly drawing his sword. Mu Li and Mu Yang also perked up, putting away their treasures and preparing for the upcoming battle.

After a while, a huge black shadow appeared before them. The shadow gradually became clearer, revealing a demon several feet tall, covered in heavy black armor. In its hand, it held a massive battle axe, ablaze with black flames, emitting a chilling aura.

"You ants, how dare you break in here and steal the treasure. Today is the day you die!" the devil roared, his voice echoing throughout the space.

Mo Xi stared at the demon without fear and said, "If you want the treasure, ask about the weapons in our hands first!"

The demon snorted coldly, swung his battle axe, and slashed fiercely at Mo Xi. The axe whipped up a gust of wind, and black flames rushed towards Mo Xi like a surging wave. Mo Xi quickly used his body skills to dodge sideways, swinging his longsword at the same time, and a sword energy shot towards the demon. The sword energy struck the demon's heavy armor, but only sparked a few times, failing to cause any substantial damage.

"This demon's defense is so strong!" Mo Xi was secretly surprised.

Mu Li and Mu Yang were not idle either. Mu Li cast a spell, and rays of light shot towards the demon, trying to interfere with its actions; Mu Yang condensed the flames again, turning them into a huge firebird, rushing towards the demon.

The demon swung its battle axe, easily chopped the firebird into pieces, while using its other hand to block Mu Li's light attack. It seemed unconcerned about the attacks of Mo Xi and the other two, and continued to advance towards them.

"This is not a solution. We have to find its weakness." Mu Li said.

The three of them fought against the demon while searching for its weakness. Mo Xi discovered that when the demon swung its battle axe, a small gap would appear under its armpits. Although it was only for a brief moment, perhaps this was its weakness.

"Ali, uncle, I'll divert its attention later. You guys wait for the right moment to attack its armpits." Mo Xi whispered.

After that, Mo Xi cast his strongest spell. The dark power of the underworld condensed into a huge black ball of light in his hand, and he threw the ball of light at the demon. Seeing the black ball of light coming, the demon did not dare to be careless. He concentrated all his energy to deal with it and swung his battle axe to smash the ball of light into pieces.

Just as the demon was desperately trying to fend off Mo Xi's attack, Mu Li and Mu Yang seized the opportunity and launched their attacks simultaneously. Mu Li infused her spiritual energy into her sword and rushed towards the demon at breakneck speed, stabbing it in the armpit. Mu Yang then concentrated all his firepower into a blazing beam, shooting it at the same spot.

The demon sensed the attack under its armpit and tried to dodge, but it was too late. Mu Li's longsword pierced its armpit, and then Mu Yang's flame beam also hit the target. The demon roared in pain, and its body trembled violently...