The first time you attack an enemy during a battle, your crit range for that attack expands by 2 (usually to 18+). A mob of mooks counts as a single enemy.
The crit range of your First Strike attacks expands by 1 (to +3).
Once per day, deal triple damage with a First Strike crit instead of double damage.
Whenever you hit with a First Strike attack, you can reroll your damage once and use the higher roll.