Red Skeleton

Red Skeletons, also known as Blood Skeletons, are enemies in the Castlevania series. Literally undead, these bloody bones always return to life. Red with the blood of countless victims.

Description
The Red Skeleton is a human skeleton stained in the blood of countless victims. It commonly walks forward steadily, and instead of dying, just collapses into a pile of bones. It will soon reassemble itself and can only be completely killed by using a special weapon or spell.

Castlevania Chronicles
Red Skeletons first appear while climbing up a series of stairs in Stage 11. A gigantic statue of what appears to be a Greek goddess decorates the background of this area. When the player finally makes it to the top, it is revealed that these skeletons are spawned from tears of blood dropping from the eyes of the statue.

These Red Skeletons in particular don't collapse into a pile of bones when hit; instead, they liquify into a puddle of blood only to regenerate moments later.

Castlevania: Symphony of the Night
There are four varieties of this enemy in Symphony of the Night:  red ,  yellow ,  green , and  white . They act in the same way as their predecessors, except their speed and regeneration rate is different depending on their color: red skeletons are the slowest and white skeletons are the fastest.

Castlevania: Harmony of Dissonance
Red Skeletons in Harmony of Dissonance are not much different than those appearing in other games; this time around, however, they are very slow and easy to be disabled temporarily. When struck, they also liquify into a puddle of blood, like those appearing in Chronicles, and recreating the scene with the Greek goddess statue crying tears of blood which emerged as Red Skeletons in that game, there's also a giant statue of a crying maiden in a room of the Skeleton Cave (Castle A).

A stronger version, called Bone Liquid, appears in some areas of the game. These have the ability to move while in puddle form and will poison Juste upon contact.

Castlevania: Curse of Darkness
Called Blood Skeletons in this game, these enemies can only be defeated by special means that may not be evident the first time they are encountered. To permanently get rid of a Blood Skeleton, it's necessary for the player to have acquired a Mage-Type Innocent Devil first and have at least one evolved into a Nautilus Rod.

The Nautilus Rod innately has the Purify ability, a spell that can permanently destroy any undead creature. The Mage-Type will cast this spell on foes, summoning a column of light that will vanish undead enemies from existence if they get caught within it. However, the casting is random and it can take a long time before the I.D. decides to cast it, so the player will often be forced to evade and defend against enemy attacks until the spell is finally conjured.

Two Blood Skeletons can be encountered in the Baljhet Mountains, and defeating them will give the player access to a room with an HP Max Up inside. This can only be accomplished later in the game, however, as the first Mage-Type is obtained in Cordova Town and the Nautilus Rod is a third level evolution, considering it has been feed the correct type of Evo Crystals.

Blood Skeletons also appear in Garibaldi Temple, on the road that leads to Legion. Gaining access to this path requires the use of a Devil-Type I.D., however, so they can only be found in the late game.

Likewise, they make a more prominently appearance in the Tower of Evermore, encountered on several floors on the way down. It is not necessary to defeat them in this location, though, and only defeating the regular enemies that spawn on each floor is required in order to gain access to the next floor, although getting rid of them first does help in clearing the room from the rest of the enemies.

Castlevania: Portrait of Ruin
Red Skeletons appear in the Forgotten City and in the Sandy Grave. These enemies yield a good amount of EXP, but one needs to use the Undead Killer whip in order to kill them.

A special magic spell known as Sanctuary can also be used to defeat these enemies. It is found in the Sandy Grave and can only be obtained after the player has acquired either the Toad Morph (found in the Forest of Doom) or the Owl Morph skill (found in the Dark Academy).

Castlevania: The Dracula X Chronicles
Tera will present the player with her necklace if she is rescued in Stage 3'. This necklace will allow to permanently destroy Red Skeletons.

Along the way, the player will come across some walls constructed with Red Skeletons' bones. If struck, they will crumble to the ground but reform themselves immediately, making further progress impossible. However, with the aid of Tera's necklace they can be destroyed for good, thus allowing the player to claim any rewards they were protecting.

Castlevania: Order of Ecclesia
Called Blood Skeletons in this game, these enemies appear in Dracula's Castle. Blood Skeletons can be vaporized by performing the Dominus Glyph Union, although Shanoa will also die.

Trivia

 * While there had been variant versions of Axe Armors in games like Castlevania: Rondo of Blood and Dracula X, called Red Axe Armors, a special version was introduced in Portrait of Ruin which behaves pretty much like Red Skeletons. If struck, they will disassemble and crumble to the ground only to reform again and continue the battle. Again, much like the Red Skeletons in that game, they can only be destroyed by allowing Charlotte cast the Sanctuary spell or by attacking them with the Undead Killer whip.
 * The Castlevania: Lords of Shadow equivalent of Red Skeletons are the Bloody Skeletons and Bloody Lancers.