The guy who played eponymous ghost in Mama is extremely tall and thin and capable of twisting and stretching out his limbs in a grossly inhuman way. By the look of his moves, one might say that creature in Mama was CGI-ed, whereas in fact it was played by the actor and SFX-ed in post-production. I think it's a good sign for Covenant, he could be even captured for the sequence - known from the green trailer - when Proto-Alien is breaking in the dropship. The positioning/sprawling of legs feels so weird there!