Just wondering about the Gargantuan thresher thing and the Woldwrath's knockdown ability.
'Gargantuan thresher power attack' is your initial attacks and doen't use the models melee weapons so doesn't get the knockdown right?
However AFAIK you can make a 'thresher' attack with one arm and a regular attack with the other right? and with Baldur (both) you can make power attacks for free.
So assuming you've been charged by a mass of infantry (but didn't lose/had stones heal) any missing branches.
1: Reposition if required and declare power attack.
2: Boost a regular attack against a model in one arc that gives you the most other models in your other arc under the 4" template.
3: Auto hit lots of other (now knocked down models) with a 'thresher' in the other arc.