User blog comment:The Dragon Demands/Season 5 trailer officially released/@comment-15030876-20150131210754

Those are not Brazen Beasts but Sons of the Harpy. They have Harpy masks, not masks of numerous animals. Also they're seen murdering people and staging a terrorist attack on Daznak's Pit against Daenerys (seen in leaked pictures for months now, and also included in the trailer for a quick shot.)