Although they were allies, the Servants of Red faction did not fully know of each other's Noble Phantasms—except for Berserker's, which was explained by his Master.

This was because his Noble Phantasm— Howl of the Wounded Beast, Crying Warmonger—possessed such an abnormal function that, in a normal Holy Grail War, would absolutely rule out his survival.

"...But, if the Servants of Black were to assault him continuously without thought, this may prove intriguing yet."

Yes, with that Noble Phantasm—allowing him to become more powerful the more damage he receives—it may even be possible for this Great War to be settled in a single night.

- Vol 1 Chapter 4