About the Stone Mask
The stone mask is an ancient artifact used by the Aztecs in rituals in order to conquer the world. The Stone mask in-game looks very unlike the mask in the anime and manga. The stone mask grants you the ability to become a vampire and gives you 2 unique moves along with it's usage. It'll give you the vampirism utility which gives you lifesteal on all attacks. The consequence is that you'll burn in sunlight without the Sun immunity ability which you can gain by using Dio's Diary when you can vampire with your stand. The item requires you to click on it to gain vampire.
You are able to use this ability in sync with your stand as well. Once you obtain vampire from the stone mask, you cannot get hamon and vice versa.
Blood Drain - You put your arm out and suck blood from an enemy through your fingers, you will regain some HP when upon using this move on a player or NPC. The health drain is considerably low so it's not recommended to use this. The move is based off of the vampire's ability to drain people and the blood drain's damage and recovery are increased by both strength and special.
Flash Freeze - Puts your arm out and freezes anyone who is in contact with the arm. The move is named after Dio's ability to freeze people as a vampire. The flash freeze freezes you for a fixed duration so it cannot be increased nor decreased.