Servants are spirits summoned by the Holy Grail to compete under Masters in the Holy Grail War. Typically, they are Heroic Spirits, beings of a higher existence given to them by the people's ideals of them, but can also be Divine Spirits, Phantoms, Wraiths, and even normal humans, in extreme circumstances.
Masters never summon the actual Heroic Spirit itself, and even to the Holy Grail or Counter Force, summoning of an actual Heroic Spirit is impossible. Only the World can directly summon the actual Heroic Spirits, and the occurrence of such is extremely rare.
When summoned by the Grail, instead of summoning the actual spirit, the Greater Grail instead records the information about the Heroic Spirits that is available from the throne, and then creates a copy of that information and forces it into the form of a Servant. In this way the Servants that are summoned are much closer to a shadow of an actual Heroic Spirit, as they are not actually the proper spirit, but a copy of that spirit based off of the information the Greater Grail has gleaned from the Throne of Heroes.
Here are the basic abilities a character can get by being a Servant.
- Enhanced Senses: Servants have extremely good senses, being able to sense other Servants even when they are out of sight.
- Immortality (Type 1 and 9): As seen in Saber Wars II event, Servants cease aging once they have hit their physical peak. Also, a Heroic Spirits true form is held in the Throne of Heroes and Servants are merely their copies, thus a Servants death will do nothing to them, though this isn't combat applicable.
- Extrasensory Perception: Servants normally can sense souls even when they are very far away.
- Soul Manipulation: A Servants main sustenance is mana, but they can consume souls to maintain themselves into the world.
- Limited Sound Manipulation: Servants vocal cords are extremely powerful, capable of creating screams that can be heard throughout the entirety of a Roman Army.
- Possession: Servants appear into the world by possessing a body or a vessel.
- Intangibility and Invisibility: By entering Spirit Form, Servants can become invisible and intangible even to other Servants.
- Non-Physical Interaction: Servants are shown to be able to affect wandering souls and ghosts, they are also shown to be able to affect conceptually non-existent body of Kama.
- Regeneration (Mid-Low; Low-Mid over time): All Servants have low-level regenerative abilities that allow them to easily heal cuts and wounds. Servants can continue fighting even with a hole through their gut and can regenerate unless their head/heart is destroyed, or they run out of mana.
- Invulnerability: Servants are Divine Mysteries that cannot be harmed by modern weapons such as guns, knives, or bombs unless they are infused with a supernatural aspect such as magical energy or possess a certain amount of age.
- Self-Sustenance (Type 1, 2 and 3): Servants are unaffected by a lack of oxygen and freely move in outer space as seen in Saber Wars and Ooku. Servants don't need food, only magical energy, and they don't starve to death, only dying when there isn't enough magical energy to keep their bodies intact. Servants also don't need sleep and can fight 24/7 as long as they are backed up by Mana.
- Acrobatics: Servants are shown across multiple medias to have insane acrobatics skills, with even someone like Ganesha able to do 720° backflip mid-air.
Here are the basic resistances a character can get by being a Servant.
- Magecraft: Servants, just like Phantasmal Beasts and Dead Apostles, have innate resistance to magecraft due to having Mystery.
- Poison Manipulation and Acid Manipulation: Servants can resist the powerful poisons of Jack the Ripper and Serenity, and they can move freely in streets filled with gaseous sulfuric acid in London.
- Soul Manipulation: Just like any other characters in the Nasuverse, a Servant's body and mind protect their souls from harm, and furthermore, they can take hits to their Spirit Origins to an extent.
- Mind Manipulation and Biological Manipulation: Servants can resist Tiamat's Sea of Life to an extent. All those who enter her Sea of Life are subject to a geas on the cellular level that makes them her minions and enemies of humanity.
- Life Manipulation and Death Manipulation: Servants aren't alive and aren't considered lifeforms, and because they're just ether in the form of past individuals and not true life, they can survive Surtr's Noble Phantasm, Loptr Laegjarn, which has a "preferential right" against all life, instantly killing whatever it hits, even Gods from the Age of Gods. Furthermore, they can see Osakabehime normally, who induces instant death with her presence.
- Transmutation and Data Manipulation: Servants can stay in digitized area in SE.RA.PH longer than humans, whereas if a person stays long enough they are turned into data.
- Absorption: Shown in Stay Night and Extella Link that Servants usually resist the effects of Blood Fort Andromeda, which breaks down everyone in the range into a bloody slurry, releasing their magical energy, and then absorbs it, only suffering a reduction in statistics instead.
- Heat Manipulation: Servants can take heat from lava and cold from a gas giant that freezes sound with minimal discomfort.
- Overwhelming Aura and Explosion Manipulation: Servants are capable of living in Age of Gods, when the mana's properties are different, making normal humans explode instantly.