"Well, the X are a parasitic gelatinous organism that when infects something, will absorb some of it's host's DNA. When it gets enough of the DNA, it kills it's original host, and creates another host, on made completely of some form of X." Samus explained. "Right, but how is it so dangerous?" Ghor asked. "Because it can rapidly reproduce inside of it's host. I almost died because of it." "Why the Metroid Vaccine?" "Turns out, the Metroid is the X's top predator." Samus explained.