As The Survivors left the temple with the Mirror of Echoes in their possession, a newfound sense of determination filled their hearts. The mirror had unveiled cosmic visions and hinted at the interconnectedness of their world with the vast universe—a revelation that fueled their resolve to confront the overlords.

Their journey took them to an ancient observatory perched atop a towering mountain. The observatory was said to hold the next artifact—the Celestial Key, a mysterious object rumored to have the power to unlock cosmic gateways and traverse the fabric of space itself.

Upon reaching the observatory's summit, they were met with a breathtaking view of the cosmos—the night sky adorned with stars, galaxies, and celestial wonders. The observatory itself was a marvel of ancient architecture, its domed roof housing intricate instruments and cosmic charts.

Ealdred, gazing at the stars above, felt a deep sense of wonder and connection. "We stand at the threshold of the universe itself," he said, his voice filled with awe.

Lirael, her archer's instincts guiding her, noticed an ornate pedestal at the center of the observatory. Upon it rested the Celestial Key—a small, intricately designed device with celestial patterns etched into its surface.

Thoren, ever vigilant, approached the key with caution. "This artifact has an air of mystery about it. We should be prepared for the unexpected."

Selene, her healing abilities attuned to the energies of the cosmos, reached out to touch the Celestial Key. As her fingers made contact, a surge of energy pulsed through her, and a vision of distant stars and cosmic gateways filled her mind.

Corin, the master mage, studied the key's intricate patterns. "This artifact holds the power to unlock cosmic gateways, allowing us to traverse the fabric of space itself. But its use must be precise, or it could lead to unforeseen consequences."

With a sense of anticipation, Ealdred reached for the Celestial Key, his fingers brushing its surface. As he did, the artifact's celestial patterns began to glow, and a portal of shimmering energy materialized before them—an otherworldly gateway to the cosmos.

The Survivors exchanged glances filled with determination, ready to step through the portal and unlock the secrets of the universe. But as they moved forward, a sudden distortion in the fabric of space sent shockwaves through the observatory.

The portal, instead of leading to the cosmos, began to unravel the very fabric of reality itself, causing the observatory's instruments to malfunction and the celestial charts to spin wildly.

In a moment of panic, The Survivors realized that the Celestial Key was not just a tool of cosmic exploration but a potential weapon of unimaginable power—one that could disrupt the balance of the universe.

Corin, his mastery of magic their best hope, tried to contain the unruly energies. "We must stabilize the portal, or it could tear apart the fabric of space and time."

Selene, her gift of empathy attuned to the artifact's energies, sensed a consciousness within the Celestial Key—a sentient entity that had been awakened. "The artifact is alive with cosmic intelligence. It seeks to protect the universe from misuse."

As they struggled to regain control, the Celestial Key's consciousness communicated with them, conveying a message filled with solemn wisdom. "You have been chosen to safeguard the balance of the cosmos. The power you seek must be used with the utmost responsibility and respect for the laws of the universe."

With their combined efforts and the guidance of the sentient artifact, they managed to stabilize the portal, preventing any further disruption. The Celestial Key's cosmic patterns returned to their dormant state, and the observatory's instruments ceased their erratic behavior.

Ealdred, his heart heavy with the realization of the artifact's true nature, spoke with gratitude. "We are humbled by the responsibility entrusted to us. We will use the power of the Celestial Key wisely and with reverence for the cosmos."

As they left the observatory, the Celestial Key in their possession, The Survivors carried with them a newfound awareness of the delicate balance of the universe. Their journey had taken an unexpected turn, and they had learned that the artifacts they sought were not just tools of power but guardians of cosmic harmony.

With each artifact they acquired and each revelation they uncovered, they were drawn deeper into the cosmic mysteries that connected their world to the universe itself. Their journey had become a cosmic odyssey, and the unexpected twist with the Celestial Key had taught them a profound lesson in humility and responsibility.

As they continued their quest to confront the overlords and unveil the cosmic truths that awaited them, they knew that the challenges ahead would be formidable. But with the guidance of the sentient artifact and the strength of their unity, they were ready to embrace their cosmic destiny and protect the balance of the cosmos.