So I have Pokemon Black and I had finally beat it when I found another HM. This HM was dive. I tried it and went into the ruins at the bottom but, what do I get down there besides items on the ground? And what's the "noise" I hear in the distance before the ruins kick me out? I really don't understand!
You find the Relic Items and the Type Plates inside the Abyssal Ruins. You can sell the Relics for high prices. The Plates can be used to boost the type they are(Spooky Plate can boost the power of Ghost type moves.), and they also change the type of Arcues to the type of the plate(Spooky Plate changes Arcues to the Ghost type.). The "Noise" is nothing, nobody really knows and it doesnt seem to be important in either Black/White or Black/White 2.