What are reminding people in the shadow that we never saw yet in the series?

After seeing Loki, a character introduced in the past, I never expected to meet him. This makes me wonder if other shadowed characters might also be revealed in the future. One that stands out is Baby 5's mother and her people, whom we haven't met yet. It felt so strange to see Baby 5's mother in shadow, especially because her silhouette looked so different from Baby 5. This gives me the feeling that we might encounter her or her people someday. Are there other shadowed characters that Oda hasn't revealed yet?