The Fuyuki Greater Grail is capable of incarnating Servants, Heroic Spirits summoned from the Throne of Heroes. Direct contact with it grants them a body that no longer requires the upkeep of a Master to exist, allowing them to become a firm existence that can remain in the world indefinitely. They still need a connection to the Master or another source of magical energy to retain the ability to use their power as a Servant, else they'll have a constitution similar to that of a human. While able to utilize their power as a Servant and Noble Phantasms with a magical energy source, they lose the ability to return to spiritual form. The body of flesh possesses the capacity to age, but abilities like Amakusa Shirou Tokisada's Left Hand - Xanadu Matrix and Right Hand - Evil Eater can work to passively confer agelessness even without magical energy upkeep.
In the case of the Fuyuki Greater Grail corrupted by Angra Mainyu, the Holy Grail Mud also has the effect of blackening the affected Servants. Only those with powerful egos capable of rejecting the influence like Gilgamesh are able to receive incarnation from the corrupted Greater Grail without being blackened as well. Servants can't normally have children because they are spiritual existences, but for a Servant who has been incarnated it might be possible.
- Fate/Apocrypha Volume 3: Triumphal Return of the Saint - Prologue
 Fate/complete material III: World Material - The Servants of the Fifth Holy Grail War:
Blackening of Servants, p.038 [T]
Blackening of Servants
The black mud in the Holy Grail contaminates the souls of those who touch it. It goes without saying for mere humans, and supernatural beings like Servants are no exception to this either. The contaminated person's personality reverses toward the orientation of evil. This is madness caused by touching Angra Mainyu. This is called "blackening". There are those who can use the black mud as part of their own power thanks to the properties of its contamination and those whose powerful egos have stayed back its mental pollution.
An example of the former is Matou Sakura and the latter is Gilgamesh. The blackened Servant is incarnated by the power of the Grail so the more concrete ties to the physical plane turns them into powerful beings.
Their physical interference power increases but at the same time they lose the ability to return to spirit form.
Also, as they no longer bother to restrain their magic energy consumption, their fighting ability jumps significantly. This momentum can be compared to a runaway train.
Because they are in that state, fine control is not possible, but in exchange, their destructive power increases.
They are fearful beings inflicting havoc and death upon the world. These are blackened Servants.
Master: Matou Sakura
Alignment: Lawful Evil
Noble Phantasm: A++
Saber Alternative, or Black Saber, is the name given to Artoria when she fell to Hassan, was consumed by the dark shadow, and obtained true incarnation during the "Heaven's Feel" route.
Artoria, now jet-black, could now invoke Excalibur without limit thanks to the enormous prana supply from the blackened Sakura. Thus, she could overwhelm Berserker Heracles even in a direct battle. Now unfettered and in a sense more powerful than she was in life, none can deny that she is the strongest Servant.
Magic Resistance: B
Lower than original value due to the corruption. Still high, as it nullifies spells at B rank (activated within three counts) or lower, and it is difficult to harm her even with high thaumaturgy.
In the maddened state while blackened, the loss of fine control makes it impossible to ride beasts; rather, the mount cannot withstand it. Therefore, in reality one can consider the Riding ability lost.
Constant self-control is required to maintain Saber's reason while blackened. To focus on suppressing her madness, her surroundings are neglected and Instinct is dulled.
Power Burst: A
Saber's body is always suffused in the energy supplied by the Greater Grail. Her armor is also reinforced, granting more defensive ability than in her original state.
The magnificent king's charm which once inspired and captivated her soldiers is gone. Since she rules by terror, leadership ability is improved but troops' morale is extremely low.
Sword of Promised Victory -- Excalibur
Type: Anti-fortress Noble Phantasm
Maximum targets: 1000 persons
Even while blackened, Artoria's greatest power Excalibur is still potent. However, the sword is tainted an ominous black. Just as the fairies of the lake (Vivienne and Morgan) manifest as both good and evil, the holy sword has its own dark side. Still, its "character" as a holy sword is greatest. The function of converting the wielder's magical energy into light through the blade does not change, but the light is transformed into the same darkness of the blade.
- Fate/stay night - Fate route - Day 15: Utopia - stay Night (II)
Fate/stay night- Heaven's Feel route - Day 15: limited. - Interlude 15-4: Death of a saint
"That gold person was showered with the contents of the Holy Grail, which connected him to it. But it couldn't taint that man, so it flowed into you, his Master. Right?"
- Fate/Zero Volume 4: Flames of Purgatory - Act 16 Part 10 -03:11:56
- Fate/Apocrypha Volume 3: Triumphal Return of the Saint - Chapter 4
- Fate/Zero Volume 2: The Mad Feast of Kings - Act 8 Part 5 -103:11:39
- Prototype material - Synopsis