This song could be about so many things, almost countless, but I believe that the "vampires" are a metaphor for depression. At that time, Gerard was going through depression and addiction and stuff like that, so I think it would be logical that he would write a song about it. "And if they get me and the sun goes down" could mean if he gets depression and he reaches a really low point in his life. "Can you stake my heart?" could mean that he's asking someone to pull the trigger for him because he doesn't have the heart to do it. "Will it fill our hearts with thoughts of endless night time sky?" obviously means death (aka suicide), and it's not just him. I believe he said "our" because that person that he wants to pull the trigger for him will be sad for a very long time, of course. "I'll never let them hurt you" could mean that he will never let that person be as depressed as him. "Fatality is like ghosts in snow and you have no idea what you're up against Because I've seen what they look like." probably means that you don't see death coming, but he did. I won't put these meanings on the "explain" thing because I'm really not sure, it's just a thought. I love this song so much, I hope I helped you out a bit. <3.