This Devil fruit is a very rare Logia fruit.
The Meiyo Meiyo no mi is accurately translated as Dark World. The user has the ability to become Dark Matter and manipulate Dark Energy at will. The dark matter the user becomes is in the form of an atmosphere. If normal unprotected life eneters this field of Dark matter they begin to burn and suffocate. Conversely if the user remains as Dark Matter too long in a light polar universe they will burn and blow away. It was eaten by the known criminal Elios the Cloudbender.
Cosmic Power: Elios creates a ring of energy and fires it in an erratic wave like pattern the attack does little damage but mesmerizes the enemy.
Makiku: The user becomes Dark Matter in the form of a caustic fog cloud
Niveous Whisps: Elios releases a cloud of glowing lights to distract the enemy
Psycho Frenzy: Disperses into atmosphere then strikes the enemy from all sides.
Psycho Pulse: Fires a burst of Dark matter/energy in a "kamehameha" fashion.
Psycho Feint: Envelopes the users body in a dark atmoshpere to temporarily become invisible long enough to close in on an enemy.
Psycho Gift: If the user is defeated dark atmosphere backlash envelopes the enemy crippling them further.
Psychosis: The user goes berserk, loss of limit inhibitors double the users attack strength.
Psycho Burst: The user envelopes themselves with dark matter/energy then explosively releasses it as a powerful shockwave in all directions.
Psycho Slash: A powerful slicing wave made of dark energy that vanishes before striking the enemy.
Psycho Punishment: The user catches the enemy in a binding blob of Dark Matter. The more they struggle the more they are damaged by it.
Psycho Target: The user remotely detonates a ball of compressed Dark energy near an enemy. It follows the enemy invisibly beforehand.
Psycho Sucker: Counter attacks the enemy before they can make a move by punching them in the gut with a fist of dark atmosphere.
Psycho Shade: The user envelopes the enemy in dark atmosphere from close range and utilizes it's caustic effects.
Psycho Wind: Blows a gust of Dark Atmosphere at the foe utilizing it's caustic effects.
Psycho Ball: Generates a ball of Dark Matter/Energy that is hurled at the enemy.
Psycho Claw: Turns the users arm into a claw if dark energy that slashes at the foe with waves of energy.
Psycho Force: The user vanishes and returns when the opponent least expects it calling down dark energy from the heavens.
Psycho Punch: Fires a punch imbued with dark energy that is invisible until impact.
Psycho Sneak: The user vanishes in a puff od Dark Atmosphere to appear behind the foe.
Psycho Curse: Attaches a glob of Dark Matter to the enemy that cripples them slowly without them knowing it.
Psycho Sensory: The user blasts the foes mind with waves of Dark Energy.
Psycho Sight: Sets up an attack that will strike the user from a distance and catch them off guard.
Psycho Gravity: Uses Atmosphere and Energy to stimulate gravity making it harder for the enemy to move.
Psycho Purge: Implodes Dark Energy to distract the enemy with the resulting burst of light.
Mist Ball: Fires a ball of caustic mist at the foe to utilize it's effects.
Psycho Beam: Fires a beam of Dark Energy from the users finger, it is very accurate.
Psycho!!!: Slams the enemy with a powerful wave of Dark Energy.
Psycho Boost: Generates a massive amount Dark Energy and strikes the enemy with it. Tires the user aswell.
Psycho Break: Utilizes Dark energy in such amounts that it breaks the air when fired.
Psycho Cut: A visible version of the Psycho Slash.
Psycho Shift: Encloses an oncoming attack in dark energy and shifts it to a new location.
Psycho Shock: Generates a powerful burst of Dark Energy that slams the enemy from close up.
Psycho Cross: Strikes the enemy in cross fashion with the users arms steeped in Dark Matter to poison the enemy.
Psycho Smog: Releases a smog of Dark Atmosphere hindering the enemy from gaining an advantage.
Psycho Shot: The User becomes Dark Matter and hurls themself at the foe.
Psycho Jab: Jabs the enemy with a spearhand made of dark matter.
Psycho Sludge: Hurls A blob of Dark Matter at the foe.
Psycho Bomb: An explosive version of Psycho Sludge making it more destructive.
Psycho Wave: A powerful wave of Dark Matter is summoned against the enemy.
Psycho Venom: Strikes the enemy with dangerous Dark Matter that increases in effectiveness if the enemy has been crippled by Dark Matter attacks already.
Psycho Blast: Pulls the enemy into a vortex of Dark Atmosphere.
Psycho Blitz: Charges the enemy at 25% power while enveloped with Dark Energy.
Psycho Bolt: While in Dark Atmosphere form the user increases Barometric Pressure to enlease a powerful Dark Energy thunderbolt.
Psycho Rush: Rushes the enemy at 50% while enveloped by Dark Energy.
Psycho End: The user launches themselves at the enemy while veiled in Dark energy and explodes on impact damaging both users.
Psycho Half: A tiring attack that severely strikes eveyone in the battle with bolts of Dark energy and atmosphere from above. The user must reert to human form afterwards.
Psycho Hold: Binds the enemy with dark energy and matter preventing them from escape while damaging them.
Psycho Mist: Slows the enemy by becoming Dark Atmosphere and surrounding them.
Psycho Rave: Strikes the enemy with spikes from below made of Dark Matter/Energy.
Psycho Charge: Rushes the enemy at 75% while enveloped in Dark Energy.
Psycho Rampage: Rushes the enemy at 100% while envelpoded in Dark Energy.
Psycho Sky: Generates a Giant Dark Atmosphere Cloud above the user and begins to rain down bursts of Dark Energy.
Psycho Storm: Generates a twister of Dark Atmosphere that the user hurls at the enemy.
Psycho Wave: Sends waves of weak Dark energy in all directions.
DarkBurst: Hurls a small glob of Dark Matter (A basic Technique)
Psycho DarkBurst: Super charges the DarkBurst and hurls it, if it splatters it may follow the enemy and trap them. (A basic Technique)
Dark World: A fusion of Dark Matter and energy that draws in all Light attributed beings and then violently collapses.
Faint Shadow: The user envelopes himself in Dark Matter/Energy and becomes invisisble temporarily.
Pros and Cons
Being a logia the user of this fruit can float by turning themselves into their element and they can ignore damage by reverting to their elemental state. This fruit possesses other qualities as well like teleportation and invisibility. However it comes witha few serious drawbacks. while it is almost universally effective it cannot be used for overly extended periods of time. The users manipulation of Dark Matter/Energy in a Light attributed world means that the users powers will fade as they fight. In addition while the user can cause heavy damage during the beginning of the fight it's attacks eventually disperse. Pure Light and wind have excellect advantages agains this fruit as Dark Matter is Weak to light as it is. In fact Light can damage the user of this fruit even when in an invisisble elemental form and hasten the waning of th users powers. wind on the other hand will aid in the dispersal of the Dark Matter into the light based atmosphere. Water, Kairoseki and Haki are all effective aswell unless the water has been corrupted by the Dark Matter/Energy making Dark Water. This fruit is cpaable of going toe to toe with the You You no Mi and can fight on advantageous ground with Blackbeard given it's caustic and slighty energy based nature. The Gura ura no Mi has little effect on this fruit because of it's gaseous and energy based states and while the Yami Yami nomi can indeed absorb dark matter and energy, it is constatnly expanding and growing and thusly will continually apply it's caustic effects. (However it has trouble expanding properly in a light attributred environment)