It depends on what you define as killing off everything. If by that we mean to kill of every single person, animal or plant, we can just continuosly nuke same place over and over again until our nukes reach magnetic core of Earth and disrupt it, which cause magnetic field of Earth to dissapear and everything to die from radiation sooner or later, well almost everything. Some things will survive and adapt to new conditions. It`s however, a temporary solution, it probably be enough to put our planet down long enough until Sun explode or whatever happens to it.

Well, we might create a black hole, but it`s unreliable solution either, because no one knows how it works. I can only say that living or being in it, if it`s possible, will be different from your or any other human definition of word "living" or "being" so that accomplishes goal of destroying everything living.

continuosly nuke same place over and over again until our nukes reach magnetic core of Earth and disrupt it, which cause magnetic field of Earth to dissapear and everything to die from radiation sooner or later

until our nukes reach magnetic core of Earth and disrupt it

Well, we might create a black hole, but it`s unreliable solution either, because no one knows how it works

we might create a black hole