[Ocellus' Perspective]
Ocellus had kept her word. She'd stopped investigating Cozy Glow, but that doesn't mean she wasn't wary of her. She trusted her as far as she could throw a bugbear. But she does trust Gallus, and Gallus trusts Cozy (at least mostly), so she's willing to give her the benefit of the doubt... for now.
Currently, she was looking out her dorm room window at the night sky. That janitor had apparently decided to start working again, for she'd seen him enter the main building about a half hour ago. Wait, what was that?
Ocellus turned her attention to the small shadow she'd noticed passing over the gardens. Then, who should descend from the sky but Cozy Glow.
She watched curiously as the young pegasus attempted to open one of the side doors. When that didn't open, she went to a nearby window and attempted to open that. No luck. After trying a couple more windows, Cozy sat on the ground and scratched at her chin as if contemplating something. Ocellus facehoofed.
'Of course,' she thought to herself. 'It just had to be her doing something suspicious, didn't it.'
She trained her attention back towards Cozy just in time to see her flutter over to a tree in the courtyard. She went around to the other side of the tree, worked a grate in the ground free, and quickly disappeared inside.
"What is she doing?" Ocellus asked the empty room, knowing that she'd have to find out.
[Cozy's Perspective]
This was supposed to be the easy part. Sneak into the school and "borrow" the book that holds the answers she needs. With the Key of Unfettered Entrance gone, she needed some other way to gain access to the object she sought.
At any rate, it turned out this wasn't going to be as easy as she'd hoped. She'd tried multiple windows and a couple doors, but it seemed Knox was quite the stickler for securing every entrance.
"Every entrance, you say," Cozy said as her mind reached a solution. "We'll just see about that."
She knew a lot of different ways to access the catacombs under the school, though she hadn't been there since her first defeat. Why hadn't she thought of this before? Going through the catacombs, she could easily access the library, which is where she needed to go anyways!
'It's probably really similar to how I remember it,' she thought as she removed the grate leading to the catacombs.
'After all, Sombra may have destroyed the tree, but it regrew, so its roots probably did too.'
She couldn't have been more wrong. The tunnels, formerly lit beautifully by thick crystal roots winding across the walls, now resembled a dark cavern with dim light emanating from what looked like shards of the roots embedded in the walls. The stark contrast from how it once looked was positively eerie.
"What happened to this place?" she asked aloud. Her voice echoed through the space as if trying to escape the terrifying scene.
"C-cozy Glow," said a crackly voice behind her.
She turned back towards the opening she'd just come through and came face to face with a strange figure.
"Wait a second... You're Harmony!" Cozy said, recognizing her via Gallus' descriptions. The figure looked like Princess Twilight, but it seemed to be made of some kind of shimmering light.
There were some obvious differences from what Gallus had described, however. The figure seemed to continuously have parts of its form fading in and out of existence. Its movements were sporadic, somewhat reminiscent of a malfunctioning robot. It's words were filled with tremors and gaps, but Cozy could understand what she was saying for the most part.
"C-cozy Glow, you m-st turn -ack. The cat-combs are n-n-n-no longer safe! Sombra d-stroy m-my connection wi-with the roots! Th- splinters are all th-t remain. You must turn back!"
"I can't do that!" proclaimed Cozy. "I have to get into the school!"
The spirit then seemed to lose connection to its own thoughts. Its next words seemed almost preprogrammed.
"Y-yes, a test. Pass the test, and y-you may go. F-fail fail the t-test..." her words faded into nonsensical murmurs before she broke out in a dark and menacing tone Gallus hadn't said she was capable of. "Here you will stay."
In a flash of light that seemed to fizzle and pop, the fractured spirit disappeared.
"Well..." said Cozy after a few moments of just standing there, staring at the spot where Harmony once stood. "That was ominous."