Shia LaBeouf -- Transforms Into Optimus Grime

Shia LaBeouf is now the proud owner of a pony, and some hardware ... in his face.

Shia debuted his Riff Raff-esque look -- ponytail past his shoulders and eyebrow piercing -- while walking around the San Fernando Valley Friday with his girlfriend Mia Goth.

It's unclear if the hardcore look is for a new movie role, or if Shia's just trying out something different.