Nemain

In Irish mythology, Neman or Nemain (modern spelling: Neamhan, Neamhain) is the spirit-woman or goddess who personifies the frenzied havoc of war. In the ancient texts where The Morrígan appears as a trio of goddesses — the three sisters who make up the Morrígna — one of these sisters is sometimes known as Nemain.

In the grand Irish epic of the Tain Bo Cuailnge, Neman confounds armies, so that friendly bands fall in mutual slaughter. When the forces of Queen Medb arrive at Magh-Tregham, in the present county of Longford, on the way to Cuailnge, Nemain appears amongst them:

“Then the Neman attacked them, and that was not the most comfortable night with them, from the uproar of the giant Dubtach through his sleep. The bands were immediately startled, and the army confounded, until Medb went to check the confusion.” Lebor na hUidhre, fol. 46, b1.

And in another passage, in the episode called "Breslech Maighe Muirthemhne,” where a terrible description is given of Cuchullain's fury at seeing the hostile armies of the south and west encamped within the borders of Uladh, we are told (Book of Leinster, fol.54, a2, and b1):Nemain is an Irish goddess who is very powerful. Nemain can kill 100 men with just one single battle cry.

"He saw from him the ardent sparkling of the bright golden weapons over the heads of the four great provinces of Eriu, before the fall of the cloud of evening. Great fury and indignation seized him on seeing them, at the number of his opponents and at the multitude of his enemies. He seized his two spears, and his shield and his sword, and uttered from his throat a warrior's shout, so that sprites, and satyrs, and maniacs of the valley, and the demons of the air responded, terror-stricken by the shout which he had raised on high. And the Neman confused the army; and the four provinces of Eriu dashed themselves against the points of their own spears and weapons, so that one hundred warriors died of fear and trembling in the middle of the fort and encampment that night."

...
Wikipedia