These kinds of prints are made with software called Hueforge. I downloaded this free model, but I might have to download Hueforge to try making my own sometime!
I'm using this pattern, https://www.savagelystitching.com/blogs/free-patterns/crochet-jellyfish-free-pattern (thanks, Vanessa!), but with regular red heart yarn, a 4.0 mm hook, and legs that are only 16 stitches long. These little guys crochet up so fast, I'm making a bunch in all different colors of yarn!