Enkidu materialising as Lancer was probably due to his Noble Phantasm. However, it was not entirely correct to call it a Noble Phantasm.
A chisel that linked the Gods to mankind, that was the true nature of Enkidu.
It was said that Gilgamesh was a chisel born to Earth because the Gods did not wish to lose power and wanted to be forever worshiped.
Maybe he forgot, or maybe he just disregarded the order, but in the end Gilgamesh did not fulfill his duty. In fact, he ruled as if to drive mankind away from the Gods.
Enkidu was the spear of discipline that was supposed to impale Gilgamesh ---- a weapon forged by Gods that penetrated all enemies and returned the Chisel (Gilgamesh) back to the Gods. As a result, there was a high likelihood that he would be chosen as Lancer by the the Holy Grail.
Also, his Noble Phantasm --- a strike that turned his own body into weapon, was most representative of his Lancer class.
He would pierce and bind worlds.
If there was a wall between the Heaven and the Earth, he would pierce it.
Just like Gilgamesh's rebellion, the Gods miscalculated again with Enkidu.
The "weapon" descent to earth and acquired intelligence through interactions with men. He wished to connect the world of Gods with the world of men in his own way. Returning the chisel to the Gods, by closing the distance between Gods and men.
In other words, the Gods shall not control men.
And men would advance to the level of Gods.
He thus chose to become a "system".
He would become the weapon of the King that ruled the mortal world, and expend himself for the purpose of advancing the world.
He chose to become a "man".
He would stand beside the King and dispel his solitude.
As the world quakes around Enkidu...
The Planet wailed.
Mana gushed from below Enkidu and engulfed the strike of Enuma Elish.
"... don't hold back."
He was not talking to the Heroic Spirit he was facing.
Like the King of Heroes talking to Ea...
He was talking to the mana that was enveloping the space-shattering Void... or rather, he was talking to the Planet itself.
"I am the weapon, wield me to your content."
In an instant, as if the gush of mana prior was just a prelude, several times more mana erupted from the ground. A tornado of magical energy enveloped Enkidu's body.
It was a concept that propagated life.
An ember formed to traverse the terror at genesis.
One that made hell paradise.
Unfazed by the separation of Heaven and Earth.
From past to future, from future to eternity.
Connecting the land and the sea to the sky.
Because life was carved with the terror of sin, men shall even purge their genes.
An amorphous mud puppet. He was a weapon and an instrument.
Walking amongst men, he was called a friend.
Since the world was already hell, humans shall make it a paradise and purge the fire of genesis.
"ENUMA ELISH (Humans, Bind Thy God)!!"
Opposite of Ea, this was a strong strike surrounded by divine wind aimed at the sky.
The Spear of the Gods Enkidu bound the torn World together and advanced forward, clashing with the Sword of Rupture Ea, which was fracturing the World around.