Prowler led the group through a small cave. Small bursts of moonlight leaked through the holes in the ceiling. The cave was eerily silent. The only noise was the footsteps of the group.

Flare let out a sneeze as a droplet of water landed on her nose. She shook it off and continued forwards, looking around nervously. 

"Why's it so quiet?" Ace whispered. 

"Would you prefer they attack?" Prowler asked, not looking back. 

The Luxray sighed. "Fair."

"What's this?" Volcan asked, stopping besides a pedestal. 

"That's a Dragonium Z. Don't touch it," Prowler responded. 

"Why not?" 

"The totem guards it. If you touch it, it will attack."

He began to walk again. "Come on."

The group moved past the pedestal. Silence fell over the group once more. Flare found herself growing increasingly nervous as she spotted eyes gleam in the darkness. 

The darkness of the cave eventually gave way to the moonlight. Before the group stood a long staircase. The top disappeared into the fog. 

"Do we have to walk up that?" Snowjoke whined.

"Get over it," Teku muttered with an eye roll. Ibuki glanced at him in surprise, but said nothing.

Prowler sighed. "Yes, if you want to get to the altar. It's not as daunting as it seems."

The Zeraora began to climb. The group followed. Ibuki carried Snowjoke. She looked down at the Bergmite and shook her head. 

After what seemed like ages, the group finally reached the top. The altar was somewhat bland. There were two small square lakes, each of which containing a smaller square platform. The water in the lakes traveled up to circle a symbol above. 

A small gust of wind blew, jostling the group. Spalding let out a small sigh, the wind ruffling his feathers. The fur on Shadow's back was raised, but the wind matted it down a bit. Even Shadow looked interested.

"Here we are. This is the altar of the Moone, dedicated to Lunala," Prowler informed. 

Flare looked at the vast canyon below. It was truly an amazing sight. 

"Pretty awesome, huh?" she asked Ace, who nodded. 

"Yes, it's really something."

Zap dipped her hand into the water of one of the lakes. The water was warm and still. 

"It's a really nice place. I can see you Alolans put a lot of effort into it," the Ampharos told Prowler. He rubbed the back of his head. 

"I think we've been here long enough."

"Really? We're leaving so quickly?" Shadow asked, looking disappointed. 

"Yes. I have this bad feeling. Like something bad is about to happen." 

"Fine," the Umbreon groaned. She got to her feet. The group began to descent down the staircase once more. Ace looked back at Teku, who was still by the lakes.

"Come on, Teku," he called. "We have to leave now."

The Banette didn't respond. Ace groaned in annoyance and turned back. 

"We need to go."

He tried to drag the Banette away with his tail, but a gleam caught his eye. The Luxray watched as a vortex appeared with a flash. From it emerged a white creature. It resembled a jellyfish of sorts. The top seemed transparent. It was covered with several white star markings. What appeared to be tentacles waved. It also appeared vaguely humanoid. Several tentacles came together to form the appearance of long hair, while four shorter tentacles resembled shorter hair and arms. Two long tentacles made up the legs of the human-shape.

Ace stood petrified, staring up at the alien creature. It hadn't appeared to spot them, as it hovered in place. 

"Ace! Teku!"

Ace turned to look as Prowler and the others came into view. The group stopped as they spotted the alien. 

"Stop! No one move!" Prowler said, holding out his arms to stop the Pokemon behind him. "Ace, do not move."

Ace's gaze flickered from the alien to Prowler and back. Above him, the alien floated down towards the Luxray. Ace held his breath, not daring to move as the creature seemed to inspect him. He silently prayed to Arceus that Teku wouldn't do anything stupid. 

As if on cue, the Banette suddenly disappeared. The creature snapped its head to the spot Teku once stood. It floated towards one of the lakes, then stopped. It appeared to be confused. 

"Teku! Reappear!" Prowler hissed through gritted teeth. There was silence.

The water of one of the lakes rippled, and the alien shot one of its tentacles towards it. It wrapped around an invisible entity. Teku reappeared from within the alien's grasp. The Banette showed no emotion as the alien floated closer. 

The air was deathly still as the alien inspected Teku. Time seemed to freeze. It wasn't until Ace began to turn red did he realize he was holding his breath. 

The alien dropped Teku and turned back to the vortex. It floated closer slowly. 

A shrill scream cut through the air. The alien froze and whipped around, as did everyone else. A Kommo-o, accompanied by two Hakamo-o and five Jangmo-o, appeared from the mist. 

"Trespassers! We know you have the Dragonium Z! Return it now, and there will be no harm done!"

No one moved. The Kommo-o cracked his knuckles. 

"Fine. We'll do this the hard way." 

He rushed forwards, aiming a punch at the alien creature. It dashed forwards, dodging his fist and circling back around. It shot a ball of sludge at the Kommo-o. The Scaly Pokemon dodged it as well. 

The guests didn't have time to marvel this fight, as they now had their own battle to fight. The dragons rushed towards the group, teeth and claws bared. 

"Try not to damage the altar!" Prowler yelled as he punched a Jangmo-o with an electric fist. 

Spalding flew above the fights anxiously. It would be rude to interfere with a battle.

"A little help here, Spalding!" Shadow yelled as she dodged an attack.

The Togekiss flapped his wings, sending a burst of air at the Jangmo-o that threw the attack. The little dragon was thrown off its feet. Shadow launched a stream of darkness at it before it could rise. 

Ace watched as the alien threw the Kommo-o to the ground. As it finished with him, Ace readied himself as the creature turned to him.  

The alien flew at Ace. The Luxray leaped out of the way and retaliated with a Thunder Fang. The alien dodged right before the attack landed. It shot its tentacles towards Ace. The Luxray let out a gasp as the tentacles wrapped around his waist. 

The alien began to drag the Luxray backwards. Out of this corner if his eye, Ace saw another pair of tentacles wrap around Teku and drag him as well. The swirling vortex got closer as the alien approached it. 

An electric blast made Ace look up. He saw Prowler and the others standing over the unconscious forms of the dragons. 

"Aim for Nihilego, but only Nihilego," he instructed. 

"For what now?" Flare asked?

"It's the name of the white creature. It's an Ultra Beast."

"I don't care what it is, I want it off me!" Ace yelled, struggling to escape. To his dismay, the grip got tighter. 

A fiery blast came from Flare and Volcan. The attacks hit Nihilego. It hissed but resumed its path. 

Prowler and Zap both released Thunderbolts onto the Ultra Beast. Ace bit down on the tentacle that was gripping him, his fangs sparking with electricity. Two Shadow Balls joined the fray, as did an Air Slash. Teku began to slash at the creature, his claws glowing with spectral energy. As the smoke cleared, Nihilego was shown to be unharmed. 

"We can't damage it!" Flare shouted. 

Ace felt his paws lift the ground. Nihilego floated in front of the vortex, its prizes still wrapped in its grasp. It surveyed the altar one last time. It turned and began to float into the vortex. 

The clink of something dropping made it stop. As it looked down, so did everyone else. There, on the ground, was the Dragonium Z.

Nihilego looked at Teku. The Banette had dropped the crystal. It looked back at it and hovered silently. Then, it dropped Teku and picked up the crystal. It examined it before turning and disappearing into the vortex, Ace still wrapped in its tentacles. The vortex swirled for a moment before disappearing as well. 

There you go! I took some of Nihilego's description off of Bulbapedia, so all credit goes to that website.