When a Spoopy is made either by manufacturing or by natural birthing methods, sometimes defects occur which will result in a Sperpy. Sperpys also seem to feel no pain as the Crème Brûlée Sperpy and Smore Sperpy are perfectly happy being burnt. At least, that's what Scientist Yoshis believe.
Yerrshers cannot tell the difference between a Spoopy and a Sperpy. They love them all the same. Sperpys are a little clueless.