The Amazing Krudsky is a simple stage magician who became a real one by absorbing the magic from Fairy Princess Willow, and yearned for more power by getting the Goblin Scepter of the Goblin King. In the end, he was taken back to the magic world by the Goblin King for torment as punishment for his crimes.
In human form: Krudsky is a short Caucasian male, balding, and overweight. He first wore a typical magician's outfit, and after gaining the magic of Fairy Princess Willow, he wore a purple and red sorcerer's outfit.
In goblin form: After Krudsky turned into the new goblin king, he was green-skinned, and bat-winged.
He is very evil, cruel, manipulative, selfish, and heartless as he wanted to become the most powerful person in the world.
Krudsky was someone who had spent a lifetime in search of real magical power, studying every spell he found and speaking every incantation in all his books, but to no avail.
Scooby-Doo! and the Goblin King
While getting ready for his magic show at the Coolsville Halloween Carnival, he was accidentally splashed by Shaggy Rogers and Scooby-Doo, who were both competing at the apple bobbing booth. He proceeded to insult them and refused to let Scooby attend the show, leading to Shaggy and Scooby getting back at him by ruining his show and exposing his tricks to the audience.
Vowing revenge, Krudsky angrily stewed in his tent, and unknown to him, Fairy Princess Willow entered Krudsky's tent, where he secretly revealed his wish to become a real magician. The fairy inadvertently caused Krudsky to notice an entry on the Goblin Scepter in a spell book. The Goblin Scepter can be combined with fairy magic to control Halloween. Taking this as a sign, Krudsky then got an idea to obtain the scepter and rule the world with it.
The fairy decided to toy with him, but while flying around, the fairy accidentally slammed her small body against a metal chair, knocking her out; Krudsky then crushed her with his flyswatter. When he noticed her cry of pain, he realized that she was a real fairy, so he kidnapped her, and used a spell to absorb her magical powers, becoming a real magician.
Later, Willow managed to escape, and hid in the magic shop of the kindly Mr. Gibbles. Krudsky tracked her down, capturing the Princess, turning Gibbles into a rabbit, and stealing various magical artifacts from the shop before leaving.
Later, Fred Jones, Daphne Blake, and Velma Dinkley observed Krudsky as he conversed with the Goblin King through a magic mirror where the Goblin King reluctantly agreed to exchange his scepter for Fairy Princess Willow at midnight at a clock tower. When Velma fell unconscious due to her rational brain being overloaded with the revelation of real magic in front of her, Fred and Daphne decided to go to the tower and set a trap for both the Goblin King and Krudsky.
At the clock tower, Krudsky and the Goblin King were almost through with their trade when Fred and Daphne released a trap and ran off with the princess. But the trap only caught the Goblin King, allowing Krudsky to take the scepter, turning himself into the new Goblin King.
After turning the real Goblin King into a goose, Krudsky and his new goblin army cornered Fred, Daphne, and Velma atop a Ferris wheel, and he used his powers to turn Fred into a vampire, Daphne into a witch, and Velma into a werewolf, respectively. At that moment, Scooby, Shaggy, and Jack O'Lantern arrived. Jack sacrificed himself to strip Krudsky of the staff which Scooby used to break Krudsky's spells, restoring his friends and the Goblin King to normal.
The Goblin King then took Krudsky prisoner for his crimes and his treachery, telling him that he'll have lots of time to "practice his act" before returning to the spirit world.