[Big Bang] Adventurer Skill Tables/Notes

I wonder if anyone knows how do these 3 skills work?

1. Mortal Blow : Does it work on boss mobs? (BigFoot, Anego, Samurai Knight)
2. Vengeance : How does one activate this skill? or Issit passive like Final Attack?
3. Hamstring : Does it work on boss mobs? (BigFoot, Anego, Samurai Knight)

Thanks !

Greatly Appreciate.