Despite the abstract drawing, Angus and Jayna could see the rough shape of the monster. It is a humanoid monster with four arms. It also has more than one face and nine eyes on the face with only one head.
Since the drawing is unclear, Angus couldn't differentiate which part is the monster's body or Anna's scribble. Angus and Jayna also know it is useless to ask Anna since her explanation only makes it more complicated.
Unless it is something that she or they directly see, Anna's explanation is very abstract, like it is dark, grass, sissy, or something. Still, Angus could feel the monster was familiar to some ancient god of war or destruction on Earth.
This is also why he feels Anna's monster drawing is dreadful. Angus is not quite superstitious, but his background and past life experience made him pay attention to these legends. He even met with the so-called God in his past life.
