The Aura of elemental mastery, epic pet's DS, is a 55pt DS..

The 2/3 penalty applies to everything in PvP.. you hit for 2/3, nuke for 2/3, etc...

Just, a "little" point was omitted, epic pet has a stun+DD spell he casts regularly, and <procs> a DD. A dual-wielder will have a hellish experience against it without a doubt (simply put, damage shields are KILLER versus duallers)