Besides the story in which Zeus turned Apollo and Poseidon into mortals once, are there more examples of gods losing their immortality in other mythologies as well? Not only in Greek Mythology.
Here is another time Apollo was made mortal. After Zeus found out Apollo possessed the full gift of prophesy, he asked him which woman would give birth to the kid that would over throw him as king. Apollo backed away and said, "No can tell pops." Zeus got so angry, he was made mortal.
The next time Apollo was made mortal, Asclepius (as a demigod) brought back a dead person for Artemis. Hades complained, Zeus killed him. Apollo got mad, he killed the elder cyclops. Zeus got mad and was going to throw him into Tartarus, but made him mortal and brought back Asclepius as a god for a compromise.