Acid Manipulation

Summary
Acid/Base Manipulation is an ability where the user is able to create, control, and manipulate acids, bases, and substances with caustic/corrosive characteristics. This includes, but not limited to:
 * Controlling the causticity of the acid
 * Where the acid/base is able to affect the object
 * How the acid/base is able to affect the object
 * The amount of base/acid being created, as well as the state of the acid (usually in liquid or vapor form)

Possible Uses

 * Acid Attacks: The user uses acids that are created, or from their surroundings to attack the opponent(s). The shape/intensity of these acids may vary depending on the user.
 * Acid Generation: The user is able to create acid on their own without an external source.
 * Acide Fumes Manipulation: The user is able to create, shape and manipulate acid is gaseous/vapor form. This ability can reach much further in comparison to acids in liquid form, as particles of gases can spread out to its surroundings faster due to its faster rate of diffusion.
 * Acid Immunity: The user is immune to acids and acid-based attacks by the opponent.
 * Corrosion/Melting of various materials, whether they are considered organic/living or inorganic/non-living

Limitations
We'll just assume that acid = corrosive substance, although corrosive substances are generally portrayed to be acids in fiction.
 * The user may be unable to create their own corrosive substance, thus can only manipulate them from already existing sources.
 * The user's ability to control this acid is essential, as loss of control of this substance can severely harm the user. Corrosive substances are able to break down the user's flesh upon contact, possibly crippling them entirely as a result.
 * The user can only control a specific type of a corrosive substance.
 * The user can only control a specific amount of a corrosive substance.
 * The user's ability to control the corrosive substance's reach, mass, precision, etc. is skill dependent. It may also be dependant on the strength of the user's abilities as well.
 * The corrosive substance can be neutralized if they are exposed to a substance that can counteract it.

Users
Credit to Superpowers WIki for this page.
 * Mei Terumi (Naruto)
 * Lava Release: Melting Apparition allows her to create strong acidic mud fires it directly from her mouth. It is capable of corroding flesh upon contact.
 * Boil Release: Skilled Mist allows her to create a cloud of mist which is extremely acidic. It is even capable of melting bodies as well as defensive techniques set up by the opponent!
 * Saiken (Naruto): Wisdom Wolf Decay lets Saiken release an extremely dense and corrosive gas that can cover a wide range in a short period of time. The gas released is strong enough that a tree is shown to be instantly disintegrated upon contact.
 * Utakata (Naruto) is able to generate an acid from his entire body, as well as capable of liquefying it. He is also able to use Wisdom Wolf Decay in a liquid state, fired as a stream of acid in this form.
 * Reptile (Mortal Kombat): This guy? He can fire corrosive acid from his mouth. Just go check out his fatalities.
 * Man-Thing (Marvel Comics), in response to fear, can secrete a powerful acid.
 * Neppa (Fairy Tail): Able to enhance his fists with acid-based powers, generating an acid upon contact as well as melting the object that it comes in contact with (the ground in this case)
 * Hendrickson (Nanatsu no Taizai): Creates an extremely corrosive acid that is able to disintegrate characters upon contact.