Any attack that involves a to hit roll and inflicts HP damage has to potential to Critically hit. On the roll of a natural 20 first this grants a +5 on the roll, just as any other time a natural 20 is rolled. The attacker then rolls to confirm the Critical hit. They roll the attack again at all the same bonuses, if it hits they Confirm the Critical Hit. There are two options when determining what a critical hit does and you may choose one of them upon confirming…
Some weapons have a higher chance to score a critical hit, represented by the Critical Range of a weapon. If a weapon as a critical Range of 19-20, this means it can score a critical on the natural roll of a 19 or 20. No attack can ever have a critical range lower then 15.
In addition most weapons will have a critical multiplier listed next to the Critical Range. the standard is x2, which means they use the rolls presented above. However for weapons with x3 and x4, use the below rules.
If another natural 20 is rolled when confirming a critical hit, the player (Not normally available to npcs or monsters) may roll to see if its an Instant Kill. if the player rolls another natural 20 then the target is instantly slain with no save, gaining the Dead condition.