Author Notes: I don't own "Undertale" and "Denny Phantom", and it should be noted that this AU of mine is entirely my own idea, so please don't hate this story that I created. So let's begin the story.
Beneath the seemingly ordinary surface of Mount Ebott, a civilization thrived – a civilization of monsters, a species long believed by humans to be nothing more than myth. For 720 years, they had been trapped within the mountain's depths, ever since the first human's fateful fall some 500 years prior.
In the damp, echoing expanse of the Underground's Waterfalls, a small skeleton named Sans ambled along, his oversized blue jacket billowing slightly with each step. Black shorts with white stripes peeked out from beneath, and his feet were encased in fluffy pink slippers, a stark contrast to the grim surroundings. He was on his way to the dump, a necessary pilgrimage for any aspiring inventor in need of salvaged parts. His glowing white pupils, a striking feature that made his eye sockets look unnervingly like real eyes, scanned the area with practiced ease.
He was searching for components for his latest project, a machine of his own design, tucked away in his basement workshop. As he sifted through the piles of discarded junk, his gaze snagged on a battered cardboard box tucked away at the edge of the dump.
"uhhh… what's this?" he muttered, his voice a low rumble. He approached cautiously, his bony fingers brushing against the worn surface. A name was scrawled across the top: 'Fenton Works'.
"fenton works? why would anyone put their name on a box?" Sans mused, a hint of curiosity in his voice. He carefully pried open the lid, revealing its contents: two blueprints, a strange green thermos, five surprisingly dry books, and a large vial filled with an equally strange, glowing green liquid.
Sans examined the items. He recognized the style of the blueprints – engineering schematics, the kind he frequently tinkered with himself. The books looked like scientific texts, filled with complex diagrams and equations. But why would someone throw away such valuable items? He pondered several possibilities:
1.Maybe it was just junk, deemed useless by its previous owner.
2.Perhaps the contents were too dangerous to keep.
Or 3. Maybe the inventor had died, their work stolen or destroyed by others, leaving only these remnants for a lucky scavenger to find.
He picked up one of the blueprints, unfolding it carefully. The intricate design, a complex network of lines and symbols, filled his vision. His breath hitched. It was a blueprint for a portal, but not just any portal – a ghost portal.
Sans wasn't fazed by the "ghost" aspect. He'd encountered ghosts before, and one was even dating his younger brother, Papyrus. What truly captivated him was the sheer ingenuity of the design. Someone had created a portal without using the CORE's magma, a feat he'd considered impossible.
"heh, heh, heh… wow," he chuckled, a genuine expression of awe in his voice. "i can't believe I found this. maybe i can finally get him out of there after all."
He carefully placed the blueprint back in the box, surprised by its surprisingly light weight despite its contents. With a flick of his wrist, he teleported – a shortcut he'd mastered over the years – to his basement workshop, placing the box on the counter. Another teleport, and he was back in his room, his mind already racing with possibilities.