As the title says that the slight chance for swords,guns and bombs to do double the amount of damage as they do on a normal swing and for the one hit kill its pretty obvious.
Critical hit:
In this any weapon would have a slight chance to do double the amount of damage as the normally do.
Conditions:The monsters who could be dealt double damage either need to be neutral or weak towards the weapon you are using.This means if you have Blitz Needle there is a slight chance that it may deal double damage to Fiends,Beasts,Gremlins and Undead.This also applys to bosses who are either weal or neutral towards the weapon.
ONE HIT KILL:
As the title says that an instant kill but with an even slighter chance to achieve.
CONDITIONS:In order to achieve this the monster must be weak towards the weapon you are using(does not apply to normal damage weapons).And also doesn't apply to bosses.
Some slight spelling mistakes please don't mind.