Can we know more about Jack and his kind??
Yes! They will appear in Vox Gothic and you'll get to learn more about them, but here's some deep lore:
Miseries are all part of underground colonies, similar to mycelium webs. Those colonies spawn their bodies when it's misty and dark.
They're born with the minimal information needed to mimic a human. When they're born they can speak but have no identity outside of what the colony gave them. That's why they all start out with the name "Jack". They gain more complex individual identities over time by eating humans.
Other colonies produce different Miseries, the one that makes Jacks is just the biggest one in Western Europe, and it's original web originated in England.
They aren't actually shape shifters. They're always physically in their monster form, they appear to be shape shifters because they use illusion magic and psychic influence to look human. Their illusion drops when they attack.
They cry when they're excited, they cannot experience sadness.
They are local to the mycelium web, but not to each other. They will sabotage and attack each other when in competition for prey or in danger of having their true nature exposed.