Casper's Scare School (2006) on Netflix

In CASPER'S SCARE SCHOOL, Casper has a new assignment: get in touch with his spooky side and start scaring "fleshies" OR ELSE! It's a tough enough challenge for the world's friendliest ghost. But when he goes to Scare School to learn his craft, he uncovers a plot by Alder and Dash, the cruel, two-headed headmaster, to take over the world. With only himself and his misfit pals Ra, a mummy with "unraveling issues," and Mantha, a zombie who can't keep her limbs on, the odds are stacked against him. But what Alder and Dash don't realize is that the power of friendliness is greater than any evil plot, and when friends work together nothing can stop them.