Ghost power weakening is the ability to render ghost powers unusable. Both ghosts and technology are capable of this feat, though it is relatively rare for ghost, and common through technology.
In "Bitter Reunions", Skulker uses the device to trap Danny, who is in Vlad's private lab at Vlad's request. The device shocks Danny, draining his powers and causing him to transform back into his human form. Danny attempts to transform back into his ghost form, but the device renders him powerless.
In "Maternal Instinct", Vlad uses the Plasmius Maximus on Danny in his Colorado chalet, effectively taking away his ghost powers for three hours until midnight. Vlad then sends his experimental "pets" to chase a human Danny through the woods.
Later, at the end of the episode, Danny uses the device on Vlad after he claims that he's still more powerful than his pets even with the Specter Deflector on. This takes away Vlad's ghost powers, and Danny sends his pets after him much as he did earlier to Danny.
In "Life Lessons", Skulker shocks Valerie and Danny unconscious by activating a bunch of devices that zap them and had placed a pair of ghost power handcuffs on them, so he could hunt them both at the same time, to disable Danny's powers.
In "The Ultimate Enemy", Skulktech 9.9 fired a blue ghost ray, known as the Phantom Palm Pummeler, that briefly deactivates Danny's powers. They state that it is completely useless against Dark Danny because he isn't a half-ghost any more and because he is too powerful than other full-ghost.
In "Kindred Spirits", Vlad traps Danny in the spectral energy neutralizer at his Colorado chalet.
- It might not work on fusions, like how Dark Danny easily ripped the Specter Deflector off while his powers were supposedly weakened. However, that instance could have been the result of Dark Danny being far more powerful than most ghosts.