Alder and Dash are the two-headed headmaster(s) of the Scare School. They started out as the main antagonists in the film Casper's Scare School, but was redeemed by the end.
Dash is the smarter, more conniving of the two, while Alder is slower on the uptake, but occasionally has good ideas. They are both rude and manipulative, and delight in causing the students and fleshies misery. In the movie, they were fed up with being the headmasters of Scare School and concocted a plan, and a potion, to usurp Kibosh and take over the underworld. Their plans were stopped by the return of their "Ankle" (Aunt and Uncle), Belle and Murray. In the series they are often full of ridiculous schemes that never pan out.