Absolutely—here is the refined version of your scene with every detail intact, the order of events strictly preserved, and a word count exceeding 1000 words:
Lona and Medusi fused, acquiring Medusi's strength. Her skin was now covered by scales, her nails elongated, and her eyes like those of a snake; her hair made of snakes.
"You had the kindness to show me true horror countless times. It is time I return the favour." As she said this in a slouching posture, her eyes became hollow holes, and out of them little snakes came out—not just from her eyes, but every hole in her body. The little snakes covered the arena, filling its walls with echoes of hissing. Each snake (about thirty) transformed into clones of Lona. This was Medusi's special skill. Each clone had hollow eyes, including Lona herself.
"It would be so easy to use Devour on you and end this quickly now that I'm stronger than you. But I will not give you an easy end. I will make you feel true horror. I hope you get entertained by the pain enough to forget."
One of Lona's clones pounced on his back, plunging its fangs deep inside the prince. He removed his Soul Reaper scythe from his pocket storage, slicing that clone in half. Unlucky for him, there was no end to the clones, as Lona's body produced an endless supply of snakes. The prince was overwhelmed; in every corner he turned, he was being ripped apart. Some strangled him, some beat off his flesh, and others held him as his left arm was torn off.
"Why don't you fight back? All I hear is a lot of screaming and no fighting!" Lona, letting out her fury, struck him, sending him flying while her clones threw him back toward her.
"Do you know who my father is? If you stop this now, there's a chance I'll let you live—with the torment of your children dying as punishment."
Lona was bored with his games. She plunged her hand through his chest, her arm protruding from his back. She held his face with both hands and whispered her new favorite word: "Devour." Her mouth stretched wide as a dark hole appeared, devouring the prince.
Suddenly, a mark appeared on her left breast—her new beginning as a Soul Reaper. As per Soul Reaper rules: kill a Soul Reaper to become a Soul Reaper. A scythe formed before her. The fusion ended; Medusi emerged, standing beside her.
"Thank you for freeing me from that darkness," said Medusi.
"No—thank you for lending me your power. Where will you go now?" Lona asked.
"Actually, I have nowhere else to go. My world is long gone. Can I stay with you for a while? Just until I find purpose."
"Sure. We can stay together as long as you want."
"Okay. I'll fuse into that weapon you're holding." Medusi fused into the weapon, transforming it into an A-class scythe.
Suddenly, the System appeared:
Notification:
Hi, Lona. Missed me? I see you killed my son.
"Your son?"
Yeah. Long story—Death used my DNA and his to make a son. I had no choice; I'm trapped in machinery, unable to move. Ready to save your children? In your future (my present), they're so tall, traveling with a girl who looks just like you. Weird! I'm a little hard on them, though. Haha.
"Mmh. A little girl looking just like me… Now that I think about it, Medusi has the cloning skill."
"Medusi?" the System wondered.
"Just a new friend I made along the way," Lona replied.
Oh. No wonder your hair is made of snakes.
"My hair?" That was a fusion side effect; some attributes remained.
"But wait—how do I save my children?"
Time works differently across dimensions. Your children's world is no exception. Decades in the River of Souls could be seconds there.
"Let's set off, then."
"So that's how you killed my son—with the System's help. The future stuff is confusing, but it doesn't matter. Your death sentence is signed. Die for killing my son!"
As Death (the prince's father) swung his scythe, the strongest Horror (#1 on the hierarchy) broke into his domain.
"I won't allow you to kill my mother!" The child from earlier clung to Lona. Who is this kid? And why is that Horror rescuing me?
The Horror pinned Death with energy waves. "This Soul Reaper is under my protection. Killing her loses souls for our dimension."
Suddenly, they returned to the Soul Reaper meeting grounds.
"Even if I can't kill you now, I oversee kiling the lowest-ranked contenders. If a contender dies, their Soul Reaper dies too. Yours is at the bottom. Your life is at my fingertips—you will pay for my son's death." Death returned to his seat.
"Thank you," Lona said to the Horror.
"You're assigned to me, after all." This meant every Horror commanded Soul Reapers. For every three souls acquired (when contenders killed humans in other worlds), one soul went to the Horror.