Berserker (White)

Berserker is the Servant you fight during the fourth round, version 2.
Her master is Monji Gatou.
She is a Funny Vamp [localized as Temptress] with disheveled blond hair and crimson eyes.
She is a fan service character.
Technically not a Servant, she is a mysterious creature that Gatou brought along from Earth. Sometimes a cat, sometimes Yuzu-nee, sometimes a silicon creature, Berserker is a princess that doesn’t seem to have a proper place in the game. She is waiting eagerly for the release of the remake.
Incidentally, in the world of EXTRA where the information world (digital) takes precedence over the physical world, she is no longer the strongest.
This is because in the information world legend becomes reality, and natural phenomena that have been incarnated as “Gods” can often hold more power than their original natural existence does.
Well even with that being said, if Berserker regained her sanity she would easily be considered a cheat-tier Servant. Her power, “The stage is the Moon, so all targets have their power reduced to a sixth of their usual” would be extremely useful against other similar cheat-tier Servants.
It’s a conceptual numerical alteration, so it is unavoidable when on the Moon. Even the Moon Cell transformed version of BB would be limited by it.
As far as EXTRA and CCC go, she‘s about the only one who can bring Golden White Face [Konjiki Hakumen] down to a level where “it’s possible to defeat her no matter how slim the possibility.”

Fate/EXTRA Material: Encyclopedia of Fate/EXTRA