Mermaids are a species of creature referenced briefly in Everblaze; Sophie finds a scroll in Edaline's office titled "Monitoring Mermaid Migration," remarking that it sounded fascinating. They're described to be eel-like, having pointed heads, with stringy, tentacled "hair" growing from these heads. They are also nothing like the human myths described.
Iggy was dyed a mermaid-like teal, ice blue, black, and purple coloring in Unlocked by Keefe Sencen.