Okay I played the game again. I suppose you're referring to the text shown in the picture below. "One snake always lies, one snake always tells the truth" is a good hint. However, I had the same text each time with the Hermes enemy.
Before the enemy transforms into the snakes, he fires blue and pink balls, but I cannot figure out which ones do damage. They are also impossible to dodge when you're up close, which is necessary to attack him.
