Rider Cu Chulainn huh. Alright, so one of his noble phantasms is his chariot, pulled by a King of horses and piloted by a King of chariot drivers. I'm guessing another is a different usage of Gae Bolg. Hard to use the one on one version in a chariot, so thrown.
My guess is that the thrown form uses the momentum of the chariot to his advantage and makes it anti army, but instead of the Lancer version, (fuck that city block), it is horizontal and Rider doesn't need to jump. Or in short, fuck that direction.
As for that last NP, the castle is apparently tied to Ireland so I wouldn't guess that. I'm guessing that either the driver and horse are separate or Ath n Galba counts.