Doodleland has a lot of rejected concepts and characters that either appeared at one point or were going to.
Tang is the largest example of a removed character. She showed up in the beta Zak and Darkclaw series, only to show up in Doodleland twice. Intended to be Zak's girlfriend, she disappeared after Little Big Doodleland and only showed up in Doodleland Wars 2 before that. She evidently knew martial arts based off her uniform and skills shown off in Doodleland Wars 2. It is unknown what she was, as a species name was never given.
The Golias were present in the beta Zak and Darkclaw series, showing up as Darkclaw's future kids. They were scrapped after Treena was introduced. Darkclaw's Golias kids have been replaced with Treena and Darkclaw's kids in the future. The main reason being that they looked like giant germs and that they weren't as intresting.
First showing up in Little Big Doodleland 3 concept art, this was scrapped after the revision. Although the Dan Planet shows up in concept art, he hasn't appeared in any thing to date, and may have been replaced with a different ship.
Also appearing in the Zak and Darkclaw beta series, he only showed up as a cameo/arch enemy for Zak. His role was later filled out with a more original character called Data Frog.
She was a idea that was created for a now-scrapped book based off mid-evil times and the Beta Zak and Darkclaw series. She was meant to be a female version of Darkclaw who worked for the Dark Side and Darkclaw might have fallen in love with her. She was scrapped permanently after the book never came to fruition.
A lightning themed cave that would have appeared in a short story arc. It would have had many jems in it, and a strange bat enemy that looked like a electrical cord that actually survived past the scrapped island.