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Out of the series I would say three are well known of and two including The Morrigan are lesser. I think this was why they lead with Merlin. He is well known and drew people in but then you have the chance to inform people about other figures in Celtic mythos.
I like Merida and Brave actually lol. You know that its set on 10th century Scotland because its the last time there were bears there. Thanks for the great reply!