Ghostly Wail

The Ghostly Wail is an extremely powerful ability. The user releases a highly destructive stream of ecto-energy from his or her vocal cords and mouth. It is accompanied by a distinct ghostly moaning sound. This power is unique to Danny Phantom and his dark future self.

Origin
In the future of "The Ultimate Enemy," Dark Danny develops this power and uses it to bring devastation upon Amity Park. Later, after meeting his dark future self, Danny gains the ability to use the Ghostly Wail himself, and uses his new power to defeat Dan.

Capabilities
The Ghostly Wail is Danny's most powerful technique. With it, Danny can cause massive damage to ghosts and humans and can destroy solid objects or send them flying. It can completely destroy ghosts that are too weak to withstand it.[1]

Dark Danny's ghostly wail was powerful enough to destroy the ghost shield that protected the future Amity Park, which no amount of Dan's other powerful attacks could do.

Limitations

 * When Danny uses this power, it drains his energy extremely quickly. Just one use can leave him with no energy left at all, forcing him to revert to his powerless human form. Inexplicably, he does not suffer this drawback in "Phantom Planet."

Dark Danny
Dark Danny uses this power in "The Ultimate Enemy" to destroy Amity Park's ghost shield. He later uses it against Sam and Tucker, but they escape by using Clockwork's time medallions to return to Clockwork's lair.

Danny Phantom
In "The Ultimate Enemy," Danny was able to defeat all his old enemies in the Ghost Zone at once with his Ghostly Wail. He later uses it twice in one battle to defeat Dark Danny.

In "King Tuck," Danny tries to use his Ghostly Wail against King Tuck's sphinx, but it fails.

In "Kindred Spirits," Danny uses his Ghostly Wail power to defeat Vlad Plasmius quickly.

In "The Fright Before Christmas," Danny destroys the entire army of ghostly Christmas trees sent at him by the Ghost Writer.

In "Phantom Planet," once Danny regains his powers, he uses his Ghostly Wail to repel all the enemies who were ganging up on him in the Ghost Zone.

Why he didn't use such a powerful technique against Undergrowth (in "Urban Jungle"), Vortex (in "Torrent of Terror"), or Nocturn (in "Frightmare") is unknown. It is possible that he didn't want to take the chance that his attack would fail against these extremely resilient ghosts, as if it did he would have been rendered defenseless.

Season 2

 * 208. "The Ultimate Enemy"
 * 210. "The Fright Before Christmas"
 * 215. "King Tuck"
 * 217. "Kindred Spirits"

Season 3

 * 312. "Phantom Planet"