Haste increases attack and spell casting speed, adds additional damage and healing to DoTs and HoTs, and reduces the GCD. Also, Haste increases your Rune regeneration speed.

Mastery provides a passive bonus to your character based on your specialization. Mastery Dreadblade increases all Shadow damage dealt, which increases the damage of core abilities like Scourge Strike and Death Coil

Versatility increases your damage, healing, and absorption done and decreases damage received.

Critical Strike increase the chance for your spells and attacks to critically hit for additional damage and healing.