As i understand it, it does benefit from mastery but in a twice removed kinda way.. the thing that determines the damage of the icicle is FB, FFB, and welly bolts which are affected by mastery. so indirectly it is affected by mastery, just not double dipping in it. I am personally wondering how its going to go with the set bonuses cause I think it will be clunky.. you get multiple FFB prods and have to use them you build up icicles really fast, then with the 2 set you build up IL after using FFB. So either you use the IL and blow your icicle charges which I think we will have to do. My biggest question really is going to be the stat prio. I think it will be still haste>mastery>crit at least until 50% then it would be mastery>Haste>crit I think. with the amp trinket it could really get ugly.. im wondering with that trinket if we should actually use the no glyphed IV.