You wrote in Insights:
(b) Perhaps Rashi's principle of "Ein Kol Chadash Tachas ha'Shamesh" applies only to living creatures, and not to fruits or vegetables. Since this is the only living creature that can be born from interspecies relations, it must have been created during Creation. In a similar vein, perhaps Rashi is only referring to items which are of essential use to man. Of such items, it is only the mule that is a novel creation. (M. KORNFELD)
What about a Koy, Chullin 80a according to the opinion that it is a cross between a Tzviya and an Ez?
When we learned the Gemara, we suggested that Rebbi Nechemyah in the name of his father held of the other opinions in Chulin, that a Koy is not a cross between two species, but is a wild Shor or another type of animal.
My answer to the mule question is that Rashi means to say that the very idea of something being created through Kil'ayim must have been nischadesh during the six days of Creation.
Shleiby, Lakewood NJ