DF Type Logia (One Piece)

Logia (自然系（ロギア） Shizenkei [Rogia], literally translated as "Nature System") is one of the three types of Devil Fruit. It is characterized by giving its user the ability to turn into a natural element or force of nature. Logia Devil Fruits are considered the most powerful as well as the rarest of the types of Devil Fruit as a whole.

Yami Yami no Mi

Strengths

An example of a Logia-user's ability to turn their
bodies into a natural element; in this case, magma.

Logia Devil Fruits allow a person to become a natural element, either in whole or in part; In their default state, they are neither completely human nor element.
Because Logia users can turn their entire body into their element, they are virtually immune to physical harm by conventional means. Any attack will simply pass through or be absorbed harmlessly into their body which, depending on the type of element, can even cause the attack to backfire on the attacker. A Logia user can be shattered, split, or otherwise separated into multiple parts, sometimes down to the size of dust, and reform without injury. The only known exception to this rule would be with Blackbeard, whose Yami Yami no Mi powers actually absorb strikes and make them stronger doing even more harm to himself than normal.

When ice and magma clashed,
the island's weather changed forever.

In addition to their ability to become their element, Logia users can generate near-limitless amounts of their element and control it at their whim, giving them fearsome attack abilities. A prime example of this class' destructiveness is when Kuzan and Sakazuki clashed with each other at full force, their Logia powers permanently distorted the weather of Punk Hazard, turning one half into a frozen wasteland, and the other half into a blazing inferno, or when Ace and Blackbeard destroyed Banaro Island during their confrontation. However, certain elements, such as smoke and swamp, are more suitable for capturing enemies rather than causing destruction.
Logia users can also use their element in other ways related to their element; Crocodile's sand power could be used to absorb moisture, Caesar Clown's gas abilities allow him to manipulate air constitutions, Enel's electricity heat could melt and reshape gold, Aokiji's ability could freeze water, and Kizaru's ability could permit him to travel over beams of light. Logia users can afford them immunity to effects related to their elements as well. For example, Crocodile and Ace are completely unaffected by the desert heat, as they possess Logia powers related to dryness and heat, respectively.
Finally, Logia users' physical strengths do not influence the power of the fruit. Regardless of the original strength of the user, their gained powers are of the same scale. This is different from Zoan fruits, which act as physical strength multipliers, and Paramecia fruits, which can be used in conjunction with the user's physical abilities. However, the properties of the Devil Fruit element can provide certain instances where the user can exploit it in conjuction with their own fighting moves. An example of this is seen the case of Kizaru, who used his light to augment his kicking strength to explosive levels

Weaknesses

“

'Logia' who think they're invincible have short lifespans.

”

— Pekoms, after defeating Caribou.

Despite the fearsome power of Logia users, they are far from truly invincible. Sneak attacks are more likely to work, as the user will not be ready to avoid them. However, with training, most Logia users learn to become their element by reflex, eliminating the ability to strike them by conventional means. For example, Enel's ability has been trained to the point that he could reflexively change form while asleep. Whether or not Logia users need to become their element repeatedly to dodge every individual attack, or can simply turn their whole body into their element for an extended period of time (possibly even after falling asleep), remains unknown.
Logia users also tend to become seemingly overconfident, as they are unaccustomed to dodging attacks, due to their intangible body. Thus, if their advantage is neutralized by some means, they have to rely on their ability to dodge, a skill which they may or may not be proficient at. This is somewhat mitigated by the fact that most Logia users shown thus far are extremely tough, even when they are vulnerable; however, for users who solely rely on the so-called invincibility while having little natural defensive power, such as Caribou, the overconfidence seems to be far more apparent and damaging.
Another way to harm a Logia is to exploit the element itself, using its properties to solidify the user and render them vulnerable to damage. For example, Enel, being made of electricity, is vulnerable to Luffy's rubber body despite his honed reflexes, since rubber is an insulator. Another example is Crocodile, who, being made of sand, can be struck if his body is dampened (either by getting him wet or striking with wet limbs), since the sand sticks together if wet.
In addition to solidifying the user's body, it is possible to use elemental weaknesses to a further extreme, completely neutralizing the element that makes up the user's body. Even though a Logia user can generate near-limitless amounts of their element, they cannot recover from blows that destroy their main "body", no matter what state it's in. This is first shown by Akainu, whose magma was able to overpower Ace's flames, causing him physical damage despite being a Logia user.
A minor weakness is that Logia users can only control their elements when generated from themselves, and not if it is in another state of matter, meaning that they cannot control their respective elements if it was not generated from their bodies. However, this could be bypassed by simply mixing their own element with a preexisting amount of that particular element in order to augment the strength of the attack (as Crocodile did with his sandstorms). Yet, this only works if there's already a substantial elemental source, such as a desert or a body of water.
Users of Busoshoku Haki can strike Logia users as if they were human; Rayleigh describes it as the ability to "force into solidity the fluid bodies of the near-invincible Logia Fruit users" when he explains it. This is not infallible, however, as both Aokiji and Akainu (Haki users themselves) have both been hit by Haki-enhanced attacks that should have injured them, but have reformed them back to normal. Akainu does mention that it is annoying to fight Haki users, though, suggesting that he took significant effort to resist it. When Haki is applied to a Logia user while they are intangible, rather than nullify the powers completely, turning the user back to their physical form, it allows the one using the Haki to grab the person in their transformed state as if they were tangible.
Finally, Logia users suffer the same weakness to sea and Kairoseki as other Devil Fruit users, forcing them back into their original form and sealing their powers.

Other information

Logia Devil Fruit users are noted for
their incredible destructive power.

Logia is an immensely powerful and almost the rarest type of Devil Fruit. The only type of Devil Fruit that is rarer are the Mythical classes of Zoans.
These Devil Fruits are not limited to the classical elements: fire, water, earth, and air, but also include physical states like smoke and sand. There are two types: tangible (something a person could hold like sand or ice) and intangible (something that could not be held like smoke or fire). Logia Devil Fruits can also be divided into two other types, forms of matter (smoke, sand, ice, lava, or swamp) and forms of energy (electricity, fire, or light). The only known Logia that does not fit into the latter method of categorization is Blackbeard's darkness. It appears that Logia users transformed in intangible elements such as light can still be pushed (as demonstrated when an explosion blasted Kizaru).
However, amongst some Logia fruits there seems to be an order of superiority. Akainu's magma completely overpowered Ace's fire. This left Ace in a state in which no medical aid could possibly hope to save him. This is an example of the danger of placing an inferior Logia against a superior one. Something almost all Logia users seem to share (except for Marshall D. Teach), is they are not used to getting hit due to being so used to their virtual invincibility, and are visibly shaken when they are harmed, despite their resilience.
Many users of Logia fruits seem to have created their own form of personal transportation and use their abilities to power these devices. Among these are Ace's Striker, a small ship powered by his flame powers, Smoker's Billower Bike, a three wheeled bike powered by his smoke powers, Aokiji's Ao Chari, a bicycle which he uses to cross the sea, freezing a small line in the water to ride on, Enel's Ark: Maxim, a ship which uses gold as a conductor for Enel's electric ability to power the ship and a Flying Gas Balloon which uses Caesar's gas ability to levitate.