Fallen Shamans return in Diablo III, but none have yet been seen in screenshots. We only know of them thanks to this animated gif, which Blizzard's D3 Community Manager, Bashiok, had in his forum signature. Fallen were in D1 and took on an expanded role with new AI, shamans, and grouping habits in D2 (Diablo 2 Fallen). How they'll progress in D3 remains to be seen, but everyone seems to like this monster type, so their return is a popular one.
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No screenshots or concept art yet.