These are spells that require the target to make one or more saving throws or be killed instantly, regardless of their current hit points. Lower-level spells usually have hit dice limits to the creatures they can affect.
“All enemies within the area of effect must succeed at a Fortitude save or die, to a maximum of 1...Wail of the Banshee
“You create a vortex of destruction that tears asunder all living things within its area of...Implosion
“A horrible phantasm rises to stand before enemy creatures in the area of effect, causing them to...Weird
“This spell destroys summoned creatures, familiars, animal companions, and outsiders in the area...Banishment
“The target creature must make a Fortitude save or die. If they succeed, they still take 3d6...Finger of Death
“This spell slays 1d4 HD worth of undead creatures per caster level (maximum 20d4). Creatures...Undeath to Death
“The target must make a Fortitude save or die. Even if the saving throw is successful, the target...Slay Living