Combat is a dangerous and
unpredictable enterprise, and sometimes combatants just get
lucky. Any character that rolls a natural twenty when confirming
a critical threat roles a third time. If this threat confirms,
the character has gotten in the luckiest of blows and instantly slain
their opponent. The opponent drops to negative hp equal to -9 or
the negative of their constitution score, whichever is
less. The character has no chance to stabilize on their own and
will die one turn later unless stabilized by an ally. Note that
no character may be slain in this manner by a weapon that is more than
two size categories smaller than themselves.
Any character that takes 50 or more points of damage and over half
their maximum hit points from a single attack must make a DC 15
fortitude save against massive damage. If a character fails the
save, they are slain by the trauma, dropping to negative hit points as
described above and dying one round later.