Skeleton is not part of the secrets, the following mobs are:
Mal0
Hornet
The Lamb
pumcat
The craftable pumpkin thingy
Do i need to explain how to get them?
I'll explain:
Mal0: Enderman + carved pumpkin head + skeleton background + making enderman cum
Hornet: Bee + carved pumpkin head + skeleton background + making bee cum
The lamb: Sheep + carved pumpkin head + skeleton background + making sheep cum
Pumcat: Craftable pumpkin girl + carved pumpkin head + skeleton background + making it cum
Craftable pumpkin girl: 8 pumpkins + 1 shears