Question: why is oogie boogie locked up?
Answer: After hearing stories about the supposed "Pumpkin King" of Halloween Town, an envious Oogie Boogie became obsessed with outclassing Jack as the scariest ghoul there is. ... Oogie's scheme was foiled by Jack, who punished Oogie by confining him to his lair beneath Lock, Shock, and Barrel's treehouse.