Question

Which statement should be revised for a more formal tone?

Poseidon, god of the sea, and Athena, goddess of war, fought for the city of Athens. Poseidon threw his spear, which produced the Spring of Acropolis.
Amaltheia was kind of like a goat who fed Zeus, which Zeus was really happy about. In fact, he turned the goat’s horn into the horn of plenty.
Chronos was the ancient Greek symbol of time. His appearance, a wise old man with a long beard, is similar to a current symbol, Father Time.
Sisyphus displeased the gods by disclosing secrets. He found himself forced to roll a heavy stone uphill, only to see it roll back once it reached the peak.

Answer 1

The second statement. It uses informal phrasing ("kind of like a goat," "which Zeus was really happy about").

Suggested formal revision:
"Amaltheia was portrayed as a goat who nursed the infant Zeus; in gratitude, Zeus transformed her horn into the cornucopia (horn of plenty)."

(If you want greater precision: "In some accounts Amaltheia is a goat and in others a nymph who cared for Zeus as an infant; in many versions Zeus later transformed her horn into the cornucopia.")