* The antique chest was as heavy as an elephant, requiring four strong men to lift it. (This emphasizes the object's weight)
* The responsibility of leading the team felt as heavy as an elephant on her shoulders. (This uses a metaphor to describe a feeling of burden)
* Despite its size, the puppy was as light as a feather compared to the grown-up dog, who was as heavy as an elephant. (This uses the phrase to create a contrast)
You can also use it in a more humorous context:
* My backpack, filled with textbooks and snacks, felt as heavy as an elephant on my way to school. (This uses the phrase to exaggerate a feeling)