story identification - 1980s fantasy cartoon, heroes go in an underground realm and free the oppressed locals, after three trials (man-eating passage, spider people, dragon)

I'm trying to remember a cartoon I saw in the 1980s. It was probably an episode of an American television show.

The protagonists end up (somehow) in an underground realm where most of the residents (who might or might not have been human) had been enslaved by an evil, magic-wielding ruler. To free themselves and everyone else, the heroes decide to venture down a guarded tunnel to recover the artifact that can defeat the evil ruler. They take at least one local along with them.

They know before they set out that there are three dangers along the way. The first is a section of the cave where the passage becomes a mouth and tries to eat them. The second is a group of web-throwing spider people, and the third is a fire-breathing dragon. I don't remember how any of the three foes are defeated, but they all are, and the heroes recover a giant ring. Then they are teleported back to the main cavern, where they have to put the ring on the finger of a giant statue, before the villain (who had gone after the heroes to stop them) gets back. When the villain does return, the ring-wearing statue shoots some rays out of his eyes and kills the bad guy.

Answer

"The Lord of Middle Earth" (1979), an episode of SuperFriends.

The relevant part from the summary:

They then run inside the Cave of the Three Deadly Tasks, in the hopes that they can reach the Magic Ring of Gandor. While on the way there they face a living, breathing tunnel and the Spider people. While they are being attacked by the Spider people, they are unable to escape their web ropes, but Batman decides to use his Bat-Laser to cut through them. But he is stopped by the Spider people. But just then, a bunch of Giant snails come stampeding and plowing through the Spider people, and therefore rescuing the three of them. They then ride the Giant snails heading toward their destination: the third and final deadly task. No one has ever survived this long in this cave! And tension is on the rise! They then discover that the Magic Ring of Gandor is being guarded by the Dragon of Darkness, the most deadly creature in Middle Earth. They manage to get to the ring, and they run back toward the Troll slave mine. But Mal Havok is in hot pursuit, and he shoots the King with a powerful magical energy blast. The king drops, seriously injured, and unable to move on his own, against the King's will, Batman and Wonder Woman refuse to go on without him, and they pick him up and continue running toward the mine.