Huh, when Grendel’s cast page described him / it / her as the monster, I didn’t think it would actually be the monster.
From it’s appearance, I think that it probably is a combat drone of some kind, possibly with living bits grafted on. Interesting to note it’s name though: Grendel. That would seem to imply that we’ll being seeing it’s creator (or mother) at a later point in the story.