Skull Boxes are the source of Torpedo Teds. They are impossible to destroy unless a star is used at the time of encounter. They have are a black box with a skull and will drop one Torpedo Ted every few moments. Skull Boxes only appear in Super Mario World and New Super Mario bros as they were later replaced with a cannon. Hopefully, their original design will be featured in future Super Mario games.
Super Mario World --> Appeared in Soda Lake and dropped some Torpedo Teds. This is the only game they appeared in as they were replaced with cannons in Super Mario Galaxy.
New Super Mario bros --> Appeared in a few underwater levels