Mike and Mabel carefully made their way toward where they knew the twisted William was waiting. As they got closer, Mike suggested, "How about you give us some cover Mabes?"

"Good idea," Mabel agreed. "Glacies! Ignis!"

The blue gem on her right wrist began to glow while the red one did on her left wrist, covering her hands with ice and fire energy respectively. Mabel clapped her hands together, causing the two energies to mix and creating a fog that began to fill the area. Since Mabel had created the fog cloud using magic, her vision wouldn't be nearly obscured by it and would be able to move undetected through it. Mike had ways to see and navigate other than just normal human eyesight, especially as he could clearly sense the twisted version of his father that was possessing Vanny. The same could be applied in reverse though as the twisted William would be able to easily sense Mike's remnant, especially in such a small confined area. But the twisted William was also in a human host, meaning that Vanny wouldn't be able to see through the fog cloud, and as Mabel is pure human, the twisted William wouldn't be able to sense her, giving the Mystery Siblings a much-needed advantage.

With a silent nod, the two split off, circling opposite sides of the room to flank Vanny. As Mike moved through the fog, he sensed Vanny shift slightly before lunging right for him. Mike was expecting this to happen though and was easily able to dodge the knife strike. Mike then struck out with his animatronic hand in taser mode, hoping to quickly shock her into submission. Vanny twisted out of the way and clamped her free hand down on Mike's arm.

"It wasn't very nice of you Michael to destroy all my minions like that," the Twisted William mocked with Vanny's voice, his dark aura starting to gather around the hand holding Mike's arm. "You can make up for it though by replacing them."

Mike gritted his teeth in pain as the dark aura suddenly forced its way into Mike's systems, trying to violently take control of Mike's cybernetics. It only lasted a second though as Mike's protective sigil tattoo began to burn intensely on his shoulder and magical energy crackled around Vanny's hand, making her and William shout in pain. Vanny released her hold and stumbled back.

"What was that!?" Vanny hissed cradling her slightly smoking hand close to her chest.

"A protection tattoo that Dipper designed," Mike said proudly, bragging about his awesome little brother. "You're not the only one out there that likes to take over people's minds and we took precautions. So sorry, but you won't be turning me into a minion anytime soon."

"And Dipper's not his only awesome sibling!" Mabel shouted as she emerged from the fog, punching a flame-covered fist into Vanny's face with so much force that the rabbit mask was knocked right off. Vanny stumbled back and swung her knife at Mabel with a snarl, but Mabel easily danced away from the strike. Mike once more tried to shock Vanny, but the possessed woman dodged and attempted to stab Mike only to be knocked off balance by another punch by Mabel.

Realizing his puppet was going to be quickly overwhelmed at this rate, William forced Vanny to retreat into the slowly dissipating fog, clearly hoping to use it as a way to hide and ambush them as they did him. Mabel and Mike once more split up, making it impossible for Vanny to attack them both at once. Mike sensed Vanny coming closer, but couldn't quite see her yet.

"I bet you think you're so clever Michael," William said, his voice echoing so it was impossible to tell where exactly it was coming from. "With all your little tricks… but I still know your weakness…"

A flash of movement caught Mike's eye and he turned to see Vanny's knife flying through the air. Mike sucked in a breath in horror as he realized it was aimed right at Mabel, who couldn't see it as she was currently facing the other way. There wasn't enough time to intercept it so Mike simply shouted, "Duck Mabel!"

"Quack! Quack!" Mabel replied jokingly as she immediately crouched down as low as she could, the knife flying harmlessly over her head where it clattered on the floor somewhere deeper into the fog. Mike barely had time to breathe out a sigh of relief before he heard Vanny right behind him.

"You were always so willing to throw yourself away for the chance to save a sister."

Mike whipped around to either attack or defend himself, but Vanny was already lunging forward. Her mouth was opened wide and William's aura filled it with many sharp teeth, all of which sank deeply into Mike's neck. Time seemed to slow to a crawl for Mike as William's twisted aura flooded into his veins like poison, paralyzing him as it went. Its real purpose though was to drain all of Mike's remnant, slowly consuming everything as it spread, including Mike's very soul. It was utterly terrifying to have such a dark twisted creature eagerly start devouring everything that you ever were and ever will be and anyone else in Mike's place would have understandably felt hopeless and powerless against such a fate.

But Mike had always been a fighter at his core.

Even when it seemed like the whole world was against him, even when he was left an empty shell on the sidewalk, even when an evil AI had attached itself to his body and soul, Mike always got up again and kept going, fighting with everything he had to try and make the world just a little less dark. So even as this monster tried to consume him in his entirety, Mike dug his metaphorical heels into the ground and said No. No, I won't let you do this. I won't let you win so easily. I will fight with everything I have!

And something buried deep inside and sealed beyond his reach cracked open just by the tiniest sliver.

Otherworldly instincts and energy flooded through Mike's body and soul. His eyes flashed yellow, his pupils became cat-like slits, and his own mouth opened to show it was full of sharp teeth as he lunged forward, fangs sinking not into Vanny's flesh but a part of William's true form that hadn't been contained in his mortal vessel. William shouted in shock and pain, Vanny releasing her own grip on Mike as William instinctively tried to jerk away as Mike began to drain him, Mike getting all his remnant back and more so. As this happened it occurred to William on a deeply instinctual level that he had big a mistake. That he had accidentally picked a fight with a being much more powerful than him.

"HEY! No one gets to do any serious necking with Kiki besides WENDY!"

Mabel's flame-covered foot slammed into Vanny's stomach as she said this, forcing Mike and Vanny apart as Vanny was knocked back several feet. With his very existence no longer in danger, the foreign instincts and power faded away, changing Mike's physical features back to normal before either Mystery Sibling even realized they had changed at all.

"UGH! Yuck! Why in the world did I do that!?" Mike practically whined as he spat out blobs of black ooze from his mouth. Without those strange instincts saying it was a good idea, Mike was just left with a lot of confusing and foul-tasting regrets. "Why would I EVER think it was a good idea to bite a monster like that? I did not need to know what essence of William TASTED like!"

"Kiki! Have a meltdown later!" Mabel shouted at him in urgency. "I could use your help here!"

Blaming nearly having his soul eaten on his absent-mindedness, Mike focused back in on the fight. While Mike had been distracted by wishing he had a water bottle to clean out his mouth, Vanny had somehow managed to pin Mabel. Mabel was lying on her back with Vanny straddling her waist with the possessed woman attempting to stab Mabel in the chest while Mabel's grip on Vanny's arm barely kept the knife from inching downward.

Mike immediately ran forward, electricity sparking between his fingers as he slammed his animatronic hand into Vanny's back. Both Vanny and William screeched in pain as electricity raced through her body and she dropped the knife uselessly to the side as her limbs spasmed. Mabel slammed her hand into Vanny's chest, the ice energy covering her hand dropping Vanny's body temperature and slowing down her vitals. Vanny and William's screaming tapered off as the host's body slumped over, prompting the Mystery Siblings to immediately stop their combined attacks.

"We didn't accidentally kill her did we?" Mabel asked in worry as she looked over Vanny's unresponsive form. Mike knelt down and placed two fingers against Vanny's neck, searching for a pulse.

"Her heart's still beating," Mike concluded to both their relief. "Though we'll probably want to heal her up once we finally free her from possession."

"Sounds good big bro," Mabel nodded as she waved her hands to make what little fog remained by now completely dissipate. Taking a quick look around the room and in various drawers and boxes, they were able to find some rope to help keep Vanny secure until Dipper could perform an exorcism.

Speaking of Dipper, he and the rest of the group came running into the room a moment later.

"Mike! Mabel! Are you guys alright?" Dipper asked as soon as he laid eyes on his siblings, immediately looking them over for injuries.

"I'm fine Dip-dop," Mabel replied easily. "But the crazy bunny lady went full vampire on Kiki."

"I swear, for being mostly made of metal now way too many supernatural creatures want to eat me," Mike sighed, gesturing to the still-healing bite marks on his neck. "But yeah, the twisted monster possessing Vanny was trying to suck out all my remnant, and nearly ate my soul in the process too."

"But Kiki got revenge by biting back," Mabel added with a giggle. "Though he seems to regret the taste of demon."

"That explains what I felt at least," Dipper mumbled before pulling out his notebook and looking at Mike with curiosity. "So what did it taste like?"

"Like burnt black licorice," Mike replied in resignation, knowing it was better just to get Dipper's questions over with now. "With an unfortunate aftertaste of a tarpit made of pennies. And I really wish I never knew this."

"I think having your soul nearly eaten excuses any bad decisions you made during the moment," Mabel assured.

"I wonder if similar creatures would taste the same or would each one have a distinct flavor," Dipper thought out loud as he wrote down Mike's response. "And would other more metal physical creatures like ghosts taste similar or would it be a completely different experience?"

"Next time we go ghost hunting we could have Kiki bite one so we could find out," Mabel suggested with a smirk.

"I am not going to just bite a ghost on purpose just so we can find out what they taste like!"

"But it would be great scientific data!"

"Yeah, Kiki! For the science!"

"I think that's enough of that," Henry interrupted, knowing that this would just keep going if he didn't stop it. "I'm pretty sure this isn't the time or place for this conversation."

"Exactly!" Mike readily agreed, happy to switch topics. "We still have to perform an exorcism on Vanny after all."

"Yeah you're right," Dipper put his journal away in disappointment before becoming serious as he flipped through his spell book. "Alright, let's clear a space and I'll paint the circle I'll need."

With their large group, it didn't take long to clear a space large enough for Dipper to spray paint a ritual circle onto. Double-checking the circle against the one in his spell book, Dipper said to those that weren't his siblings, "It's probably best if all of you stand pretty far back. I've only performed exorcisms on ghosts so I'm not quite sure how this will go, so it's best to be extra cautious."

Henry and Michael immediately began herding all the children back, finally settling at the doorway to watch what was about to happen. Mike and Mabel quickly positioned the still unconscious Vanny in the center of the circle before taking their place a few steps behind Dipper. As soon as his siblings were clear, Dipper began to chant, his eyes and the circle lighting up with magical energy. At first, Vanny only twitched a little as the spell was being spoken, but as soon as the first part of the ritual was complete, black oozing smoke practically exploded out of Vanny, letting everyone see the inhuman monster Mike had been able to see this whole time. The twisted William let out a bone-chilling snarl as it began attacking the barrier created by the circle, using enough power and force that cracks were starting to appear.

"He's stronger than I was expecting," Dipper cried, forced to one knee from the strain of trying to maintain the spell. "He's going to break out before I can banish him."

"Looks like Dipper needs our help Kiki," Mabel said, holding out her palm to Mike. "Let's lend him our strength."

Mike nodded and used his claw to cut Mabel's palm before cutting his own. They quickly went around opposite sides of the circle until they formed a triangle with Dipper, both of them slamming their bleeding palms on the edges of the circle. The circle began to draw on their strength as well, Mike's veins beginning to glow as his remnant reacted to the large amount of magic he was helping channel.

With his sibling helping to take some of the burden of keeping the twisted William contained, Dipper was able to start the second half of the ritual. The twisted shrieked and withered as the spell took hold, finally disappearing in an explosive wave of energy that knocked the Mystery Siblings onto their backs and even those in the doorway stumble as it passed over them.

The abrupt silence that came afterward as the spell completed and the glow faded from the circle was jarring but brought a sense of victory and relief that it was finally over.