Northrend Beasts-
Anti Magic Shell- Soak toxin and bile damage on phase 2 aswell as poison clouds. Soak breath if you are good at timing in phase 3.
Tanks- If you watch your timers, you can soak up the paralyzing toxin when they dig up the second time (the one which usually ends up with a tank stunned).
Lord Jaraxxus-
Anti Magic Shell- Soak legion flames, soak infernal eruption and their damage.
Faction Champions-
Anti Magic Shell- Usable once you have a few dots or to soak hellfire.
Twin Valkyr
Anti Magic Shell- Usable anytime during the fight. Also can help you soak other orbs.
Tanks- Use when the opposite colored one does their aoe.
Anubarak
Anti Magic Shell- Usable if you get the white scarab debuff to a few stacks, usable if you have penetrating cold, and usable at anytime in phase 3 to negate your personal boss healing.