A lot of times, even though the element itself may not show up to breed, most specials are made from commons. If you research the element from past you'll see which commons were needed to get it. Ex: skull trio sugarskull glider was first - earth and nature required 13 hrs, then skeletal steed needed nature and fire 16 hrs, third was dead wing where before u bred sugarskull with skeletal steed you could definitely try nature/fire/earth combo using no other element in the mix.
Usually it's worth a try to breed for sale animals, you could get lucky