Place the ice cream, milk, vanilla extract and a small drop of blue food coloring into a blender and pulse until smooth.
Pour the milkshake into tall glasses.
Place the freshly whipped cream into a piping bag or a Ziploc bag and snip off the tip, creating a large, round tip.
Pipe a swirl of cream on top of each milkshake and garnish with a mermaid shell and mermaid tail.