In truth, your friend only ever really found 1 so-called mystery, the "troubling figure on the water" but they had to find a way to dig deeper, to sate that curiosity and get Hardwin to come out of hiding. So they made the other ones up.
You're here because you're curious too, are you not? Then please, keep following down the rabbit hole, see where that leads you.
You know the code at this point, have you tried it on everything? You may want to go over some repeat areas.