According to the 5e PHB:
"Tieflings are derived from human bloodlines, and in the
broadest possible sense, they still look human. However,
their infernal heritage has left a clear imprint on their
Why then, if what most basically makes them Tieflings is an infernal heritage, can't there be non-human Tieflings, I.E. Infernal/Gnome, or Infernal/Elf? Would there be any known way to stat such a creature?