Grey Alien Horror

I saw it lurking around outside. Thought it was a kid but suddenly it stood up fully, it's legs and arms were longer than I had assumed in the dark and although it initially looked just like those aliens from comic books and tv, it wasn't remotely human like those cartoony depictions, it was truly otherworldly. Like something that's always existed and was just overlooked. It dragged something off the ground into the dark- I watched it's shadow as it opened it's mouth and lifted the figure above it's head, it's mandibles splitting open from beneath expelling an organ that enveloped it's prey