Simple

Only then did the Ancient One notice the faint blue energy darting through the surrounding space, while the hand Mercer held beneath the Tesseract remained completely unchanged.

This was not the original gymnasium!

From the moment the Ancient One stepped inside, she had already been in a separate dimension created by the Tesseract.

Just as Mercer had said, this space he had constructed with the Tesseract was entirely under his control.

Within this space, all teleportation magic had ceased to work!

Gripping the Ancient One by the throat, Mercer slammed her viciously into the ground.

The tremendous force sent spiderweb cracks spreading outward from where she landed, a testament to the power of that blow.

"Urgh!"

The Ancient One coughed up a mouthful of blood. Her body could not withstand many more blows of that magnitude.

"Bastard, don't underestimate me!"

Layers of black-and-gold circular Magic Arrays sprang up in the Ancient One's hand, containing immense magical energy that she was about to fire straight into Mercer's face.

Before she could unleash the magic, however, Mercer stamped down on her hand at lightning speed, crushing her Magic Arrays beneath his foot.

The bones in her hand broke as well, and she cried out in pain.

The Ancient One was the Sorcerer Supreme. Drawing on Dormammu's power had made her far stronger than before.

If the Avengers had come to stop her, even a lucky victory would have ended in horrific casualties.

Mercer knew that perfectly well, so he never held back to feign weakness. Every attack was meant to kill.

After all, she had already tried to harm him once. Did she really expect him to show mercy?

Mercer was not a bad person, but he was no fool either. He would never do something that stupid.

"You damned bastard!"

Fine beads of sweat appeared on the Ancient One's forehead. A faint black light glimmered over her chest, but instead of gathering for a moment before firing as it had before, it exploded immediately.

The massive explosion made Mercer instinctively leap back a short distance, and the Ancient One seized the chance to put some space between them.

Escaping right now is impossible. I need to at least give him some trouble first, or I'll never get out.

With that thought, the Ancient One let out a low shout and slammed both hands against the ground.

A dozen or so gold and black Magic Arrays formed beneath her hands. She lifted them into the air, then swept her palm downward.

The Magic Arrays erupted with powerful beams of magical light that shot straight toward Mercer.

"Heh. That's all?"

Mercer smiled faintly. He no longer even bothered holding the Tesseract, using lightning from the Rumble-Rumble Fruit to support it instead.

Whoosh-

With a thought, he activated the Tesseract's power. Just before the incoming magical beams reached him, they vanished into thin air like stones sinking into the sea.

As the Ancient One stared in shock, the space beside Mercer rippled, and magical beams identical to the ones she had fired shot out of it.

The Ancient One neutralized the beams with a grim expression. They were every bit as powerful now as they had been when she cast them.

The tremendous magical energy left even her reeling. Mercer had used the Tesseract to redirect those beams back at her.

Magic of this kind had become completely useless against him. No matter how much she used, it would only rebound on her in the end.

"The Space Stone's powers are such a pain!"

The Ancient One's expression darkened. She was already at her wits' end. All the spells she used had been created based on the Book of the Vishanti.

Though their effects differed, they all operated on the same principles.

The Mangekyo Sharingan had long since been active in Mercer's eyes. Whatever magic the Ancient One used, he could see through its core at a glance.

Could it be those?

The Ancient One noticed his even stranger eyes. Could those eyes actually see through every spell she cast?

That was absurd!

Even if he had learned magic, he should not have been able to counter every move on sight.

Could Mercer have already reached a level beyond magic itself?

Damn it, this man is a monster. He mastered the Book of the Vishanti in less than a day. Damn it, I really picked the wrong person to cross this time!

The Ancient One cursed inwardly. Not a trace remained of the effortless composure she had shown when they first met.

If Mercer had not learned the Book of the Vishanti, the Ancient One might not have lost to him. But it was far too late for that now.

Mercer had sealed the space, leaving the Ancient One unable to flee. Her mastery of magic was no greater than his, either, so she could not even fight back.

Subduing the Ancient One proved almost unimaginably simple.

Restricted at every turn, she had no chance of defeating him.

Punch after punch struck the Ancient One's face. Whatever method she tried to escape with, Mercer thwarted it before she could get started, leaving her helpless to do anything but take the beating.

A few minutes later, Mercer held the half-dead Ancient One by the throat with one hand, his eyes full of pity.

"What a shame. I thought we could become good friends. I never imagined you'd lose sight of who you were because of the benefits dark power brought you. You're so very different from the Ancient One I knew."

"Please, please wait. I surrender. Let me go. I'm willing to follow you. Just spare my life!"

The Ancient One spoke in despair. She could sense the growing killing intent in Mercer's words. If this continued, he really would kill her.

After hearing that, Mercer rubbed his chin and nodded thoughtfully. "I am indeed immortal, and you still have your uses."

The Ancient One's face lit up, thinking she still had a chance. She was about to press her advantage and say more when Mercer continued...

"You made me fight it just now. Now you can go in and try it yourself. If you can survive in your current state, go ahead and try."

"Huh...?"

Mercer snapped his fingers. The Tesseract, suspended beside him by lightning energy, rippled with blue energy and opened a portal.

As he spoke, several tentacles seemed to writhe on the other side of the portal. Mercer promptly threw the Ancient One inside.

The tentacles reached through the portal and caught the Ancient One, immediately wrapping around her and pulling her inside as though afraid she might escape.

Mercer closed the portal at once, a faint smile lingering on his lips.

"You really are ruthless, throwing her into that monster's lair. We just pissed it off. Who knows how furious it is now?"

Galacta's airy voice came from beside him as she landed lightly at Mercer's side.

"I'm just returning the favor. With the Ancient One taking our place, that Great Old One probably won't come to our world to bother me anymore."

That was Mercer's plan. Having had so many tentacles chopped off by him, the Great Old One was surely furious. Leaving things as they were might lead to a second Great Old One invasion of Earth.

Sending a scapegoat to suffer in their place should soothe at least some of the Great Old One's anger.

If it still came after them later, Mercer might no longer be weaker than it by then!

"Hehe, none of that matters now. What matters is what we're going to do with these tentacles." Galacta pointed at the tentacles Mercer had severed nearby and looked at him expectantly.

"Of course... we're keeping them for ourselves. With all this delicious food, why would we give it to anyone else?" Mercer said with a smile.

Galacta jumped up like a delighted little girl, already working out how to divide those "squid tentacles" from the Great Old One with Mercer.

Whew-

With everything settled, Mercer let out a long sigh of relief. Things should finally be over for now.

This battle had not only thwarted Hydra's greatest scheme but also eliminated a hidden threat.

"Whew. Surely I can finally get some proper rest now?"

Before Mercer could even catch his breath, the system's voice suddenly sounded in his mind.

"Mission triggered: rescue the Ancient One!"