DuckTales has featured more references to Disney animated canon than any prior Disney series. More than just exploring the world of DuckTales itself (which has included references to classic stories like, "Christmas On Bear Mountain," and the return of Goldie O'Gilt), and answering long-held questions like whatever happened to Della Duck, it's also been incorporating various characters from other Disney animation properties into its universe.
LUDWIG VON DRAKE
First introduced in the television series Walt Disney's Wonderful World of Color, Ludwig Von Drake became a consistent presence in Mickey Mouse and Donald Duck cartoons. He typically appeared whenever Donald's family was involved, or whenever a character needed some kind of absurd technology to play with. While the character did appear in the original DuckTales cartoon, the new series ties him closer to the overarching world of Ducktales.
Ludwig Von Drake first appeared in flashbacks during, "From the Confidential Case Files of Agent 22!" as the chief director/scientist of the secret altruistic organization, SHUSH. By the present day, however, it appears that Ludwig has passed away. In "Raiders of the Doomsday Vault!" Scrooge is seen speaking with Ludwig's family in an attempt to secure a contract protecting Drake's vault containing relics from around the world. He only appears in that episode in the form of video messages, which act as helpful guides for people trying to explore his vault.
THE GUMMI BEARS
Disney's Adventures of the Gummi Bears premiered in 1985. The series centered around a small group of anamorphic bears living in secret near a human castle. Set during medieval times, the Gummi-Glen Gummis are the last of their people, left to try and protect the secrets of their kind from the forces of Duke Sigmund Igthorn. His intention is to use the protected Gummiberries to make Gummiberry Juice. The elixir can give the drinker supernatural powers -- most notably the ability to briefly bounce around with incredible speed and strength.
Also introduced in, "From the Confidential Case Files of Agent 22!," the recipe for the Gummiberry Juice is revealed to have survived into the modern day. The scientist Black Heron (who works for SHUSH's villainous counterpart FOWL) attempts to reproduce the serum (saved in an ancient text, along with a picture of the bears), to use in her attempts to help conquer the world.
Although she does manage to make the potion, Webby is able to steal the serum away from her and ingest it herself, giving her the bouncing powers and allowing her to help stop Heron. The end of the episode reveals that Webby managed to make off with some of the potion, and Mrs. Beakly actually memorized the recipe before she destroyed the parchment containing the secrets of the concoction.
TaleSpin aired in 1990, recasting many of the animal cast members of The Jungle Book as an assortment of air pirates and plane couriers. The series focused on the town of Cape Suzette, where Baloo the bear works as a delivery pilot on a plane called the Sea Duck and sometimes crossed paths with the likes of Shere Khan, the kingpin of Khan Industries.
One of the most consistent villains was the sky pirate, Don Karnage, the cocky captain of the massive Iron Vulture. Karnage and his crew of sky pirates made the transition to DuckTales in the episode, "Sky Pirates...In the Sky!" They attack the Sun Chaser (the plane flown by LaunchPad McQuack for Scrooge) and manage to steal all of the treasure on the ship.
However, Dewey briefly manages to usurp him as the captain of the Iron Vulture. Don is a significantly goofier character in the new DuckTales, obsessed with being the star of lavish musical numbers during his heists. But, he's still a surprisingly cutthroat villain, at one point even kicking a disappointing henchman off his plane. The episode ends with Karnage vowing vengeance on Dewey, implying he could eventually make a reappearance.
THE THREE CABALLEROS
For a period of time during the original stretch of Disney animated shorts, Donald Duck actually usurped Mickey Mouse as the studio's biggest star. When Disney wanted to make a film to promote the connection between Latin America and the United States, they produced Saludos Amigos. The film centered around Donald and his Brazilian friend, José Carioca, exploring South America. The success of the film led to a sequel, The Three Caballeros, which also introduced the Mexican Panchito Pistoles.
The trio has appeared together infrequently over the years, most recently in the animated series, Legend of the Three Caballeros (which has a separate continuity to DuckTales). The trio also made an appearance in DuckTales, recast as Donald's old college band that were reunited in, "The Town Where Everyone Was Nice!"
All three gave up their dreams of becoming famous musicians as life shifted around them in unexpected ways. But, the group were still on hand to save the rest of Donald's family from a carnivorous plant monster by putting on one more performance of, "The Three Caballeros," the theme song from the film of the same name.
Darkwing Duck ran from 1991 to 1992. The series centered around Drake Mallard, an otherwise unassuming suburbanite who was secretly the gadget-heavy superhero, Darkwing Duck. Although the series was disconnected from the original DuckTales (which was confirmed to be the case by Darkwing Duck creator Tad Stone), it did feature some characters from DuckTales, including Gizmo Duck (who was Darkwing's unwitting superheroic rival) and Launchpad (who was recast as Darkwing's bumbling but loyal sidekick). It also heavily focused on Drake's adopted daughter, Gosling, and his sorcerer girlfriend, Morgana Macawber.
Initially, the current iteration of DuckTales established Darkwing Duck as an in-universe fictional character. The main actor on the show, Jim Starling, was even voiced by Jim Cummings, the voice of the original Darkwing. In a nice nod to the original series, Launchpad is revealed to be a massive fan of the series.
In "The Duck Knight Returns!" he meets a fellow Darkwing geek who'd been cast to play Darkwing in a new film adaptation of the show. When Jim goes off the deep end and tries to take the role back by force, the actor and Launchpad stop him.
At the end of the episode, Starling is believed dead, and the movie is canceled. But, Launchpad suggests that the actor could assume the Darkwing identity in the real world and become an actual superhero. It's only then that the actor reveals his name -- Drake Mallard. Meanwhile, Starling survives an explosion he set off but goes mad in the process, becoming this show's version of Negaduck -- the original Darkwing Duck's answer to the Joker.
As an added bonus, the episode of the old Darkwing Duck series that's featured in "The Duck Knight Returns" includes a shot of the St. O'Malley's Kitten Orphanage. This could be a subtle shout-out to The Aristocats, a Disney animated film about a street cat named Tom O'Malley who helps save a family of pampered Parisian cats after they're abandoned.
A GOOFY MOVIE
The Goofy Movie was a direct-to-video animated film released in 1995. It was essentially a follow-up to Goof Troop, a more traditional animated sitcom from 1992. Both focused on Goofy as a humble single father to his son, Max. The Goofy Movie focused on their time together when Max is in high school. Goofy forces them to go on a road trip so they can bond. But, a sullen Max is furious that he's going to miss a concert by the pop star, Powerline, and the chance to hang out with his crush, Roxanne.
DuckTales has slyly referenced Powerline twice, both in connection to Dewey. In "Raiders of the Doomsday Vault!" Dewey and his recently returned mother Della sing, "Stand Out" which was one of Powerline's greatest hits in The Goofy Movie. Dewey is later seen performing the "Perfect Cast" (a fishing technique Goofy and Max accidentally taught Powerline as a dance during the climax of the film) in "The Duck Knight Returns!" suggesting that The Goofy Movie indeed is part of the DuckTales world.