Whenever a backstab deals at least 10 damage, the assassin's foe is riddled with bleeding wounds that inflict 0.25 x [backstab dmg modifier x (weapon dmg + attribute bonus to dmg)] dmg over the next 4 seconds. Exploit weakness dmg is added to the backstab dmg computed above before being multiplied by 0.25. If the assassin also has Shadow Striking and Shadow Form is sustained, the total of the backstab dmg and exploit weakness is multiplied by 1.5 1st before being multiplied by 0.25.
Lacerate is completely bugged and has no effect. When determining if the effect is applied, the game checks if the player has a modal ability with the lacerate ID active, instead of checking if the player has the passive skill. As such, the check will never succeed and Lacerate's damage over time will never be applied. An unofficial fix for PC can be found here