The Dust of Dengeron is an item that was shown in the episode "The Tale of the Super Specs".
The item is a magical powder that enables people who aren't actually magically inclined to successfully cast simple, but effective magic spells. Also
there is a downside, this magical powder can cause mayhem and total destruction depending on what spell the person is casting. As seen in the episode, Weeds didn't know what he was doing.
When he fooled around with magic, he didn't realize that with this powder he successfully casted the spell of second sight which enabled a doorway to parallel universe to open. Also this powder enchanted a bunch of sunglasses called Super Specs, which enabled whoever was wearing them to be able to see beings from another universe entering and attempting to take over.
Eventually Weeds' girlfriend aided the help of Sardo, used this powder to try and counter the spell and send the alternate world back to their own space. Sardo however wasn't a very experienced magician, as he attempted to finish the spell to close the window and send the alternate world back. Then a powerful dark phantom, known also as The Dark Lady, intercepted Sardo's spell and switched the spell onto their world instead sealing the real world away and letting the alternate world take over that space.