Intangibility

Summary
Intangibility is the ability to pass through things physically. Characters with this ability are simply unaffected by attacks, as they pass through their bodies. This can also allow them to pass through walls and other physical objects.

The exact mechanics of intangibility differ depending on the individual, and may have to be activated in order to take effect. Many characters cannot interact with objects when intangible.

Intangibility users should preferably have their method of intangibility specified on their page, as the workings can be countered through different means, depending on the type.

Here are some examples of the many varieties of intangibility:

Elemental Intangibility: The ability to become intangible by transforming into a substance, such as wind, fire, or water, making it so that most attacks merely disperse them instead of truly damaging them, allowing them to regenerate. However, this would still leave the user vulnerable to many forms of attack, such as sufficiently powerful energy or elemental attacks.
 * Users: Juvia Lockser and Rogue Cheney (Fairy Tail), Sandman (Marvel Comics), Logia Devil Fruit Users, such as Smoker (One Piece), Suika Ibuki (Touhou Project)

Immaterial: This type of intangibility allows the user to phase through most attacks due to not being made up of a physical substance, such as ghosts or characters who merely exist as a disembodied soul. It also includes characters that are made up of things like energy. Of course, this intangibility type still has its own weaknesses - a soul is vulnerable to soul manipulation, for example.
 * Users: Lille Barro (Bleach), Danny Phantom (Danny Phantom), Servants in Spirit form (Nasuverse)

Phasing: The ability to phase through matter by becoming briefly intangible, sometimes through such means as vibrating one's molecules at such a speed that it becomes possible to move through physical matter. This includes doing things like altering your own density to phase through objects. However, this does not necessarily allow the user to phase through immaterial energy-based attacks.
 * Users: Flash and Superman (DC Comics), Stands (JoJo's Bizarre Adventure), Shadowcat and Vision (Marvel Comics)

Spatial: The ability to shift into other dimensions so as to avoid and phase through attacks. While this allows them to avoid most forms of attack, they can still be affected by attacks that operate on similar principles and by those with sufficient range to target them in the other dimension.
 * Users: Obito Uchiha (Naruto), Reimu Hakurei (Touhou Project), Ahzek Ahriman (Warhammer 40,000)