jabberwock (fate)

Jabberwocky:

The Jabberwock
And as in uffish thought he stood,
The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
And burbled as it came!

One, two! One, two! And through and through,
The vorpal blade went snicker-snack!
He left it dead, and with its head,
He went galumphing back.

(Jabberwocky by Lewis Carrol)

Nursery Rhyme can summon the Jabberwock (ジャバウォック, Jabawokku?), a being she calls a "friend" that is greater in power than Servants. It is initially believed to be the Berserker-class Servant of Alice, and it has an overwhelming presence. It uses a skill called Alice Eater (ありすイーター, Arisu Ītā?) to temporarily strengthen itself.
Its strength shakes the Arena itself, and simply nearing it allows for its fierce, swirling magical power to be felt. It can overwhelmingly defeat Hakuno Kishinami's Servant, and the only defense is to retreat because Alice doesn't have it to pursue them due to wishing to wait for Hakuno to "play" with her. It is created through their power, and it will stay until its granted magical energy is depleted. In the Fate/EXTRA Manga, it was shown that while Saber and Lancer could damage the Jabberwocky, it simply regenerated from its injuries, even restoring its decapitated head with no issue.

It can only be defeated by the Vorpal Blade, a "blade of legend that no one has ever seen", a Mystic Code weapon that has an effect on certain types of monstrosities. It is from the poem Jabberwocky by Lewis Carrol, depicting a nameless hero's quest to slay the fearsome beast. It is not something found normally within the Moon Cell, but crafted by an alchemist with Malachite. The one created by Rani VIII is only able to be used once. It emanates magic as it nears the Jabberwock, shrinking his aura and allowing for him to be defeated in regular combat.

https://typemoon.fandom.com/wiki/Nursery_Rhyme_(Noble_Phantasm)