Well since you posted link for first video of WotN i guess you saw in it 6:25 when he open hero screen, there is `wife`(sexy blonde with long braid
) with 4 of her friends in item slots. I`m thinking those are valkyries that join you during game. 6:26 if you have eagle sight and know russian, translate what are her bonuses when he pass with mouse over wife portrait.
I think every valkyrie will give you some bonus when you acquire her throughout the game, something like kids in the Legend