The power to
have innate physical armor for protection.
The users has or can generate an innate armor as a part of their body, which is resistant to attacks, harm or pain and temperature extremes. The armor varies from obvious, physical defenses, such as scales, thick skin/fur, natural shield, armor or shell, in-organic skin, etc, to bone-nodules below skin, particularly wide/sturdy rib cage, blubber, or simply dense muscle.
Weak against Deoxygenation.
Depending on how heavy armor users may sink in water.
If one were to disrupt the process of "armoring up" the results would be user losing the ability to armor up for quite awhile.
Selective armoring is rare, in short it is an "all or none" principle, either fully armored or not at all.
May sacrifice speed for durability.
Reverting back to original form or natural state may be moderately difficult or irreversible.
Greed (FMA: Brotherhood) is known as the Ultimate Shield due to his Carbon Dermal Armor.
Alex Mercer (Prototype) in his armor.
Indra (Marvel Comics) in his armor.
Bling! (Marvel Comics) deflecting bullets off her skin.
The Hulk's (Marvel Comics) skin can withstand virtually anything.
Skaar's (Marvel Comics) skin has incredible durability.
Due to cellular degeneration, the Guardian's (Marvel Comics) skin is five times as dense as the original Spider-Man's.
Ethan James' (Dino Thunder) skin is impenetrable.
Kakuzu (Naruto) can change his skin to harder-than-steel earth armor.
The Third Raikage's (Naruto) body has earned the epithet of the "Strongest Shield" due to it being near-impenetrable, which, when combined with his Lightning Release Armor, is even more so.
Ryūichi Sendō (Code:Breaker) turning his skin's texture to steel and other hard substances to block attacks.
Tetsuhito Kagiroi (Tenjho Tenge) possesses an iron-hard body due to his clan's women drinking iron sand every night.
Rhydon (Pokemon) has a powerful rock-like skin.
Skarmory (Pokémon) has a powerful steel-like skin.
Jozu (One Piece) has diamond skin when he wants to.
Monkey D. Luffy (One Piece) using Busoshoku Haki to darken and harden the skin of one arm.
Skin Bolic (D.Gray-man) can change his skin into a golden armor of solidified lightning.
Tōkajin (InuYasha) implanted Shikon shards into his body, turning it into an armor of stone.
Nnoitra Gilga (Bleach) using Hierro to pressurize his spiritual energy onto his skin, turning it iron hard.
A Quincy (Bleach) such as Ichigo using Blut Vene to flow spiritual energy into their bloodstream, turning it inhumanly hard.
Cang Du (Bleach) lives up to his epithet, "I - The Iron".
Samedi endures being thrown into a car unscathed.
Gatasubal (Yu Yu Hakusho) is composed entirely of a hybrid metal of combined steel and living cells, making it very difficult to pierce through
True to his surname, James Ironside (Blood+) can harden his skin to the point where it can easily withstand bullets and blades...
in Senator Steven Armstrong's (Metal Gear Rising: Revengeance) body harden in response to physical trauma, granting him nearly impenetrable skin.
Mutikapa's (Utawarerumono) fur is so tough that it can withstand virtually anything, including attacks from super weapons.
The NKVDemon's (DC Comics) skin has been artificially hardened.
Judoon's (Doctor Who) thick skin allows them to be impervious to most physical attacks.
Torafusa (Fairy Tail) can alter the density of his skin that can not only stop Gajeel's magical iron but break it as well.
Iktotchi (Star Wars) possess thick skin to protect them from the high winds of their homeworld.
Guilmon (Digimon Tamers) possesses such thick skin that Renamon's Diamond Storm attack bounces right off of him.
Ghouls such as Ken Kaneki (Tokyo Ghoul) have such thick skin that conventional blades break if they try to pierce it.
Luke Cage (Marvel Comics) has such thick skin that a thug breaks his hand trying to punch him.