A phrase I heard this week I found evocative: a "demon seed."

A thing with awesome, overwhelming potential within it, but currently packed up into a little, unassuming, dormant seed.

In the right environment it would blossom explosively and change the world.

This trope shows up in horror often: the evil spellbook sitting there latent, waiting for someone to open it.

The overwhelming power and potential need not be evil or malevolent, it could just be awesome, in the original sense of the word.