Sapphire Styx was a mutant capable of draining others’ life force to power her own. That worked out for her for quite a while but she tangled with the X-Men once too often.
References: [wikipedia.org: Sappphire Styx]
[marvel.fandom.com: Sapphire Styx]
[writeups.org: Sapphire Styx]
not[crystal]