Here's the breakdown:
* It's a power inherent to ghosts: All ghosts, including Danny, have this ability to some degree. It's a powerful sonic blast that can be used to stun, knock back, or even shatter objects.
* Danny's unique control: While other ghosts might use their Ghost Wail instinctively or with limited control, Danny has exceptional control over his. He can focus it, shape it, and even use it as a shield. This is because of his human side and his training.
So, Danny doesn't *acquire* the Ghost Wail, it's part of his ghost DNA. He simply learns to use it effectively through practice and understanding.