Perseus and Medusa
So Perseus flies up to the island of the Gorgons and enters the cave where Medusa was sleeping.1 He knew that looking straight at her would kill him, so he used the reflection in his polished shield to sneak up on her. Perseus sliced off Medusa’s head and put it in the sack he’d been given to prevent accidentally looking at it. 2 Out of Medusa’s blood grew the flying horse, Pegasus, which some people find improbable, but I think is a whole lot more likely than being able to sneak up on somebody while looking at their reflection in a polished shield. If you’re looking at someone’s reflection, you have to be facing the opposite way. If you think it’s easy to do this while sneaking up on somebody, try it and let me know. Naturally, Medusa’s two sisters were furious and gave chase, but Perseus put on his helmet of darkness and became invisible and so escaped, which begs the question, why didn't he just have the helmet on the whole time.
1. The myth is not clear if this was at night. Maybe Gorgons just slept a lot. If your expression turned people into stone, you wouldn't get out much.
2. He may have been dissappointed when he got the bag as a gift, but I bet he was sure grateful to have it now.