Van Augur had stitched the arm back when Vash returned. Blackbeard sighed in relief. He was a darkness human, and light was his weakness so in time of day or in the presence of light he couldn't turn his body into darkness like other logia.(A/N: I'm using a fan theory I read somewhere) He was trying to use Mythical Zoan fruit in his darkness form before he was sneak attacked. Blackbeard was confident of beating every enemy that is why he didn't run after losing an arm. He was already in Yonko Commander level in power with only Darkness-Darkness fruit, and now he also ate Mythical Zoan Thunder Roc devil fruit becoming Yonko Level threat. The strength that Blackbeard possessed now was tremendous, his reaction time was upped, and most importantly, he could now create and control all kinds of thunder.
"Zehahaha... You will be first to have a taste of my new power." Blackbeard contemptuous words were followed by huge boom of lightening, his body slowly morphed into an grotesque looking bird. Vash who was observing from the distance felt feather grew out from the fat rotund man; lightening crackled around upper limbs which had also turned feathery. Blackbeard's mouth morphed into a beak, feet turned into claws, his cloths also stretched and grew to cover his enlarging body. He became 15 feet tall abominable monstrosity.
Blackbeard utilized hybrid form of Zoan devil fruit right off the bat. The feather growth on his hands were razor sharp.
It was dark of the night without any natural sources of light, as dense clouds had covered the moons, and the artificial sources of brightness from human settlement were destroyed by Van Augur. Vash had to use Color of Observation to know what's going on, and the whole scene in front of him felt as if an apocalyptic beast Darkness-Thunder had awoken, bringing storm of destruction.
"Hmph... You will regret eating the fruit." Vash put two and two together, and knew that the ones in front of him are in cahoots with the ones he killed before. He knew they must have come here for the devil fruit. So he didn't want to waste anymore time and attacked.
*Buzz*
The swords hovering around Vash spun in high speed, they became red hot and after some time, the sword blades got covered in plasma like thunder liquid. Vash was going all out to kill the man in front, he had simultaneously used all three types of haki.
"Aargh... What's this light?! It stings." Blackbeard said. What he didn't like most was light. He was omnipresent in darkness and could teleport to anywhere dark, although it had limit of maximum distance of more than a kilometer. But in a fight, this skill was invincible. But ultimately, the light emitting from sword disabled him from the use of teleport.
Although Vash had no problem fighting in the dark but he impulsively lighted the swords. He used Color of Armament to create light, and radiation implied explosiveness thus countering darkness. He had no idea of the weakness of his opponent, but when he saw uncomfort on Blackbeard face he came to know of it in due time.
"Damn you... Put that light out!! Volatile Blackhole!!" Blackbeard shouted. The darkness physically manifested in front of Vash pulling him into it. The force of attraction was like a star exerting immense gravity.
Two swords glowing with light vanished and appeared within the mass of darkness. The blackhole exploded instantly, but the exploding darkness got erased by energy emitting from the swords before it do any damage. The swords also crumble after becoming brittle.
Vash stepped forward. He held same two swords which he made previously: A katana and a Western short sword. Instead of being flamboyant like other hovering swords, these two gave off faint lights. Vash hacked out a compressed air blade using the katana, Blackbeard dodged it but flying slash's target was Van Augur, who was hiding in the back after the fight started. Van Augur was preparing a sniper rifle of old model. He wanted to annoy his enemy from the distance.
The flying slash's speed was like teleportation. Van Augur couldn't even react. His body was bisected horribly. He died quick.
"Shit... Van Augur!!! You guys are useless!! It's better you lot are dead and not my subordinates anymore." Blackbeard said in anger. He was flying above the ground after the evasion.
"Dark Matter Wave!!" Blackbeard shouted as surrounding darkness turned into gooey substance. This substance was like plague, it grew more by swallowing objects. After consuming rubble and debris, it turned into tsunami like waves, and crashed toward Vash.
"Really dangerous at the same time disgusting." Vash said and swiped horizontally with his western short sword cutting the wave in half. Although he had cut it, the dark matter was still falling to his position so he flew up but few drops still fell on him. Vash used Armament Haki to protect himself, patches of lightening flickered on his skin destroying anything getting too close. Vash then moved his arms in a gesture that suggested he was lifting immense invisible weight.
"Zehahaha... What are you doing? Are you frightened so much that you became an idiot." Blackbeard mocked Vash. Blackbeard was still controlling the move and the cut waves reformed into bigger wave eating things on the way.
"Hmph... I told you, you will regret it." Vash said as he made throwing posture with his raised hands. But nothing really happened immediately.
"..."
"..."
"Zehahaha... what clown---" Blackbeard was cut short as he noticed something coming towards the location, and he ran feeling uneasy, like his abilities encountered a natural enemy, it was more dreadful than light. But Blackbeard couldn't outrun the huge bubble of seawater falling. So he enveloped himself in dark matter wave and braced for the impact.
The bubble of seawater didn't splash, Vash held the spherical shape with Supreme Kings Haki, After that it changed into hemispherical dome, making ground a circular base. The seawater came from the bay of the city, it effectively trapped Blackbeard.
*Sizzle**sizzle*
The 'dark matter wave' enveloping Blackbeard was slowly getting destroyed by seawater as smoke escaped the water dome.
'Dark Domain' Blackbeard released more substance from his body, this time he used enormous amount of his stamina to generate it. The seawater and the substance annihilated each other completely.
"Haah... Haah..." Blackbeard was tired. Vash was also somewhat mentally exhausted, but they continued to fight.
Gleaming swords of light raced aiming for Blackbeard; extremely fast and accurate. Blackbeard flapped his wings, congealing darkness with it. The swords shattered and exploded on contact with dark element. Blackbeard was thrown off and injured from the shockwave.
Vash appeared in front of Blackbeard with glowing Katana held in his hand. He was extremely fast. Blackbeard wasn't able to react as he was not his hundred percent, but he defended using his claws at the last moment. Vash had used every ability in his arsenal to deliver a powerful attack.
*Shing* "Aargh"
Blackbeard screamed in pain, two claw fingers each from both legs were cut off in tandem with sizeable chunk of meat and bones from upper legs.
Vash didn't give him any mercy and was about to finish off the opponent when his Observation Haki alerted him of impending danger. Vash quickly backed off as a grey thunder fell at his previous location. He then looked up in the sky which was covered in dark clouds; lightening swam the clouds like serpent venturing forest.
'Shit... I would have been goner if it had hit me.' Vash thought. He saw that Blackbeard's body grew again as he fully transformed into mythical bird with wingspan of 30 m, The head of the bird resembled eagle with sharp curved beak. Though it had no talons.
"Trying to escape now." Vash got future sight, he clearly felt the intent of the huge bird--- it wanted to escape.
"Aaaaah... You cut my leg!! I kill you!! Thunder Rain!!!" Blackbeard shouted as countless bolts of lightening rain down on the town; he was controlling the thunder clouds. Some of the lightening also hit Blackbeard but it didn't do any damage, but it seemed as if he was energized instead.
The number of bolts were uncountable and fell down endlessly, Vash could easily disperse clouds but thunder bolts were relentless. Vash concentrated and stabbed a lot of swords in the ground, they acted as lightening rod, attracting electricity. Vash got brief period of respite from falling bolts and he kicked upward, creating a compressed air blade. The air blade grew enormously as it traveled upward. It parted the clouds and dispersed them.
"Phew... the lightening stopped, but the culprit ran." Vash said. Blackbeard had left when Vash was busy dealing with lightening. Vash felt Blackbeard leaving his range of Observation Haki but he didn't bother giving a chase because he knew he wouldn't be able to catch up as Blackbeard was flying in his Zoan form and was using 'Darkness Teleportation'.
"That was one tough opponent!! I'll have to up my training if I want to thoroughly crush him in future." Vash muttered to himself.