38 seconds into the "Character Development" video shown at GDC, there is a brief image of a mysterious figure, clad in a hooded black cloak, antlers, and holding some kind of 'staff.' If the five panel "mood board" from the GDC presentation is anything to go by, then this figure may very well be a member of the as-of-yet unseen fifth race of enemies (possibly named the Glimmer?).
This seems a plausible deduction to me as the yellow tone, black smoke, and white-faced black figure parallel the fifth image in the "mood board" quite nicely.
Also (and this is a thinner comparison), the triangular shapes in the yellow "mood board" panel are similar to the triangular "ships" seen in another piece of concept art revealed at GDC (one that Bungie won't talk about yet), and the antlered figure's cloak does have a rather triangular hood...
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We're talking race 5. Looking at the shadowy blob in the I would guess they're like the 'anomalies' from S.T.A.L.K.E.R. and must be killed by some special means. The bipedal figure is some evil leader that can control the blobs. Alternatively, They are all bipedal, and have a shadow-disperse when they get shot at for self-defense. They poof around in battle to get behind you and attack.