For those of you sleeping under a rock, we're currently experiencing a time space phenomenon of absurd proportions.
At thus moment in time even immortals are killable. Based on who you are, this is either great news or a catastrophe.
Basically, if you're an immortal and die within the next ~week, your past self, one prior to you becoming immortal, will die. This will ensure your death.
If you happen to be part of the immortals, just take a vacation to an alternate timeline.
If you happen to have a grudge with an immortal, now is the best chance you'll ever get.