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

Agility increases your attack power and the damage dealt by your abilities.

Mastery provides a passive bonus to your character based on your specialization. Mastery Potent Poisons increases the damage done by your poisons.

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.