April's mind was a whirlwind of confusion, panic and shock, trying to decipher in a matter of seconds what just happened. Had she moved a little bit faster; This wouldn't be happening. But it was, and she knew from that sinking feeling in her stomach- that it was far too late to do anything about it.

They were too slow, and now they had to pay the price for their actions. Their leader collapsed to his knees, knuckles white and panting heavily. Then he started to shake violently.

Mikey was the first to react, crashing forward to his fallen, seizing brother and trying to pick him up without touching the ooze. It covered his skin so intensely, he looked unrecognizable in the sludge, "Leo!" He cried urgently.

"Oh no..." April choked out, unable to form any proper sentence. She felt that horrible feeling of dread inside her again, and it didn't seem to be leaving anytime soon.

"No, no, no, no!" Raphael charged passed them both, chanting erratically like a mad man. Lisa was close behind, looking equally as scared.

Donnie was the only one who hadn't moved. They seemed to be taking a longer time to register that the mutagen had in fact hit Leonardo; when the actual assault was intended for them instead. They shook their head furiously, ripping their purple mask and bandanna off and frantically attempting to cleanse the red eared slider of the ooze. "Are you crazy? Why'd you do that? That's mutagen, you moron!"

Leo weakly lifted his head, "Couldn't let you get hit," He chuckled, falling into a coughing fit shortly after, "What kind of leader would I be if I did? Or brother."

"A dumb dumb, that's for sure," Donnie shot back, tears leaking down their cheeks even with snappy reply.

"Is he gonna be okay?" Mikey asked anxiously.

"Do I look okay?"

"His body is already starting to change..." Lisa examined Leo's arm, watching as flecks of gills started to scatter.

"You all better listen to me right now," Leo slapped Lisa's hand away to prevent any ooze from landing on her, "If I- aah...transform or some shit, ya gotta make a run for it. Maybe leave this ship, it's been nothing but trouble."

"No way!" Raph refused, "We ain't going anywhere without you."

"'Sides, we can't do anything without our leader!" said Mikey.

"There must be a way we can prevent you from turning..." April said thoughtfully. "Dee? What do you think?"

Donnie looked on the verge of a breakdown, muttering to themselves as they tapped on their tech gauntlet, "I can fix this, I can fix this, I can fix this!" They looked directly in their twin's eyes, sharing a connection even as their brother held back a strangled scream, "I swear, I will, Leo just hang on a sec buddy-"

A horrible howl of agony echoed through their ears- Leo's scream caught everyone off guard as the transformation truly began before their very eyes. He shoved Donnie away, rougher than he intended; gasping and wheezing for air- as if he was losing the airways to his lungs. "S- Stay back!" He yelled, his voice sounding deep and croaky; "Don't wanna hurt you-" His eyes went wide before he fell to his knees; seizing once more as foam formed his lips. He was convulsing in a crumpled heap, breaths becoming shallow and inconsistent.

"Donnie, what's happening?" Raph demanded, hoping the seizure would stop. But it only got worse.

Claws started to grow from his fingernails, sharp and pointed. Each finger shook in excruciating pain, blood dripping from the ends as Leo let out another awful scream. His toes and hands were longer and flatter now, as though they were webbed like that or a fish's fin. Gills shifted on his neck, thigh and biceps- looking equally as painful.

"He-" Donnie backed away, trembling with fear as Leo's howls and tears shifted into a deafening roar. "He saved me. But now he's-"

"Make it stop, Donnie!" Mikey begged, trying his best to stay close to Leo, who's condition was only worsening. "Please!"

They all knew what was happening; and they all knew Donnie did not have any answers to solve it.

"Donnie!" Raph repeated urgently. "What is happening?"

"I didn't think it was possible!" Lisa gulped.

"He's mutating..." April whispered, the only one able to say it.

The transformation was longer than any of them had ever expected with normal mutations. It was slow and excruciating as each of Leonardo's limbs morphed and contorted into a completely different shape; bones cracking, shell melding into his skin and finally: his legs fusing together to form one slender, fish tail with silver gills scattered on it.

His snout was pointed, with sharp teeth growing out of his large mouth. His skin was still green, but now had patches of icy blue from his armour, plastron and carapace fusing into his body. He was sleek and serpentine in appearance; and his black eyes had no pupils whatsoever, but his red markings by his cheeks remained trickling downwards.

He barely resembled the same turtle, hell, he wasn't even a turtle at this point.

"Leo...?" Mikey whimpered, calmly walking towards the sea serpent, hand outstretched to lightly pet his brother's snout. "S' gonna be okay..."

Leonardo's eye slits darkened, unable to recognize the little turtle with his warped mind. He hissed like a snake, flicking his tail threateningly. Still, Mikey made no sudden movements. He wasn't afraid of his brother, even now.

"Mikey, no!" Donnie pulled him back. "He's not the same anymore!"

"Stop, let me go!" Mikey shoved his sibling away furiously, eyes filled with tears. He smacked Donnie's arms until they finally released him, "He's my brother! He's our-"

The mutant hissed.

"He's our brother."

"An' we aren't gonna hurt him," Raph assured him. "I swear."

"Then what are we gonna do?" Lisa asked, yelping as Leo snapped his jaws at her. "He's out of control!"

The humans that remained outside now were screaming at the newly transformed mutant. They ran around in circles, causing an obvious commotion.

"What is that thing?" someone asked.

"It's a sea monster!" someone else hollered.

"I don't know," Raph said, putting on a brave face. "We could try to tie him up, maybe April you could calm everyone down?"

"Now hang on a second!" April said. "We have to find that Fish Freak and make him turn Leo back pronto!"

"If anyone can turn him back, it's him!" Mikey agreed, "So!" He pointed at the fish who seemed to be standing quite still. "Cough up the answer!"

Filch looked positively delighted, strolling towards Leonardo ready to boast at his success and ignore Mikey, "He's perfect! Even better than I imagined! A vicious beast ready to do my bidding. Unfortunately he seems a bit mindless but..." he waved a hand casually. "I'm pleased with the results. Aren't you?"

"You!" Raphael roared, pointing his sai at the fish with a glare, who didn't even flinch. Filch seemed strangely casual for someone who made a monster, and Raph was furious, "You better turn him back right now!" His remaining siblings did not bother pulling him back- Fishface deserved whatever was coming to him. The normally docile turtle was not willing to play nice.

"Ha! Even if I could, I wouldn't!" Filch snarled, "My plan may not have gone as I anticipated, but now I've got a sea monster as a pet! So really it was a win win...

"Plus spreading a little chaos is what I do best," He laughed with glee as Leonardo roared once more, chasing a group of people.

"You're not gonna touch him!" Raphael growled, charging towards him with a murderous look in his eye. He tackled the mutant to the ground once more, pinning him and refusing to back down- even as he heard the snap of bones. He didn't care if he had to wipe blood off his hands or snap this monster's neck in half. He would pay for what he did.

Something rolled underneath Raph's leg, falling out of Filch's satchel carelessly from the initial attack. He ignored it and threw another punch at the fish's temple. Lisa scooped the object from the floor and pocketed it, but Raph was blinded by the sudden rage to notice.

Fishface flicked his tail, smacking Raphael in the face. "You can attack me all you want, but you must face the fact that your brother is no more," There was a mischievous glint in his eye that further enraged Raph. "He belongs to the sea. And me."

"No! Even though you mutated him, he'll never, ever, join you, Fishfreak," he snarled back.

"Uh, Raph?" Donnie poked their head from behind, biting their lip, "We have a problem."

"Can't it wait? I'm about to smash Filch!" Raph snapped. "Keep an eye on Leo."

"That's the problem!" Mikey squeaked, "He's going haywire!"

Raph stopped his punches to turn around, heart plummeting to his stomach.

There was an animalistic growl followed by a hiss. April seemed determined to tie Leo up with Mikey's nunchuck chains- but the mutant had now increased in size and strength.

How could he have been so focused on getting revenge on Filch; that he had failed to notice his brother was getting worse?

"It's not gonna work," April yelled, narrowly avoiding Leo biting her head off. "He's too strong!"

"And fast!" Lisa added.

"An' uh Fishface got away..."

To his left, he turned and saw Fishface had indeed wriggled out of his grasp, "Any more bad news?" Raph asked dejectedly, watching as Leo tore open what looked like the hull of the ship. He bit it in half and chomped down hard. Water spurted sporadically and the boat started to shift filling with freezing water. If the people on the ship weren't panicking before, they certainly were now.

"Yes, actually," Donnie grimaced. "Leo just...ate the bilge pump so now it's leaking."

"Which means...?"

Waves crashed over them, screams filled their ears before finally dissolving into darkness.

"This ship is sinking."

There was not a second to waste. Already people were swarming like insects to lifeboats. But the gang, even Lisa stayed put. Time was ticking, and if they didn't find Leo soon- they would sink with the ship.

"We can't leave without Leo!" Mikey said, stubborn and distraught. Even as sea water was filling up to his ankles, he couldn't show that he was afraid.

Lisa climbed on Raph's carapace for extra height, "We don't have a choice, not when the boat is sinking!"

"It'll sink in precisely two hours and forty minutes," Donnie said, giving April so she could climb on their back securely. "What do we do Raph?"

Raph looked at his odds. Leo was rampaging about on the ship. The ship itself was doomed to sink. He wanted to save everyone- including Leo but he didn't see it being possible. The double mutant was huge, and much stronger than he was. Not to mention, his sense of mind seemed to be hanging by a thread.

He never considered he would have to make this choice.

He looked at his younger siblings' wide, terrified eyes. "I...we have to go. We'll take that lifeboat over there," He gestured with his thumb at a lone, slightly rickety wooden boat that looked ready to break in half.

Mikey looked predictably outraged. "No! Not without Leo!" He stormed over to tug on Raph's arm like a little kid. When his brother didn't budge, he looked desperately at Donnie, "Donnie! Tell him!"

Donnie shook their head, wincing as they all heard Leo's growls. "Mikey..."

Another wave crashed into the mighty ship, causing Mikey to topple over like a bowling pin. They were running out of time. And judging by the sounds Leonardo was making, he didn't seem eager to go with them.

"We don't want to leave him either, but I think Raph's right," April said, helping Lisa on to the lifeboat. The two girls had yet to have a single conversation, but that didn't seem to matter. They were a team now. They all were.

"We'll turn him back," Lisa vowed, although she had no idea how they would do that. "I think we will."

Mikey refused to move, still fixated on finding Leo.

Raphael gave in, having to lift his screaming and sobbing baby brother into his arms, wordlessly assuring him that everything would be fine. Even though the lifeboat was starting to drift away into the middle of the sea. Even as the clouds turned into mist and the waves knocked their boat away from everyone else's.

Even as they saw a flash of Leonardo's fish tail disappear into the ocean and out of sight.

There was no telling if everything would be fine ever again. Only time would tell.

"Leo..." Mikey murmured, half asleep as he leaned into Raph's plastron.

"At least we know he escaped that monster," Donnie said, jolting slightly from the waves hitting the tiny boat. "I hope."

April hummed in agreement, a yawn escaping her.

Wherever Leonardo was, he was away from Filch.