The Prydain Chronicles
Alright as far as sources go. See if you can find this book at a library.
An Introduction to Celtic Mythology by David Bellingham
Great 128 page soft cover book that really gives you the basic myths and description of deities and provides all it's sources. As far as I know it is part of a series as I picked up it and a book on Viking Mythology that was part of the same series.
Irish Fairy & Folk Tales W.B. Yeats What the Grimm Brothers were for the black forest Yeats was for Ireland. These are his actual poems and stories so you have to interpret them for yourself but they are a good read and they will get you in the mood for a celtic game.
The Prydain Chronicles
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