The super-starch is an invention by the villain costume designer. It is to be sprayed on articles of clothing to give them the ability to stand up without being worn, move around on their own, and act autonomously. Despite being a chemical highlight, simple everyday fabric softener can undo its effects.
Done with being underpaid for designing and producing outfits for the criminals of St. Canard, the villain costume designer developed the super-starch to take matters into his own hand. The super-starch is a grey liquid stored in an ordinary spray bottle. When applied to clothes, they come to function as if they were worn, but with a mind of their own. This mind seems to have qualities of the people they were designed for, but is subservient. To whom is not clear, as it could be either the person applying the super-starch or the person who made the costume. The villain costume designer made the villain costumes and brought them to life after which they were loyal to him, and the same is true for Darkwing's costumes, which he presumably made himself, to the crimefighter after he sprayed them with the super-starch. It is unknown if the super-starch wears off over time, but its influence can be countered with regular fabric softener.
Disney Adventures comics
After missing out on years of proper payment from his customers, the villain costume designer decides to take matters into his own hands. Turning to chemistry, he develops a super-starch that when sprayed on clothes makes them mobile and sapient. With this, the designer creates his own army of villain costumes consisting of the outfits of Ammonia Pine, Steelbeak, Tuskerninni, the penguins, Negaduck, Megavolt, Quackerjack and an unknown number of Eggmen. Most of them are sent out into the streets of St. Canard, while the Negaduck costume assists the designer in robbing banks. The mass hysteria in response to costumes walking around without people in them draws the attention of Darkwing Duck. The crimefighter finds himself outnumbered by the costumes of some of his biggest enemies, but he hatches the idea to try fabric softener against them. Victory comes easy with this tactic, leaving him free to follow the screaming to the final costume and the designer, who's brought his bottle of super-starch with him. The designer sics the Negaduck costume on the crimefighter, but Darkwing uses the fabric softener against it. The designer tries another dose of super-starch, but Darkwing thwarts his plan with another round of fabric softener. Launchpad McQuack then confiscates the super-starch to end the fight. When the police takes the designer into custody, Darkwing holds onto the super-starch for own use. That is, he sprays three of his own costumes with it to do various jobs around the garden for him.