Mermaid Costumes Make Your Own DIY Mermaid Costume! The following websites and video offer tutorials on how to make a homemade mermaid costume for a baby, infant, child or adult! Mermaid Costume Tutorial – Creative Green Living Learn how to make a last minute mermaid costume – no sewing skills needed! DIY Infant Mermaid Halloween Costume – The Pinning Mama How to make an easy no sew infant mermaid costume. Use fun colors and patterns to make it your own! Mermaid Tutu Dress – The Hair Bow Company DIY Mermaid Tutu Dress perfect for Halloween or birthday parties!