Over twenty orcs, annihilated in one go. Holy shit.
This is the nemesis board, after all is said and done:
Granted, Schreckstoff had already killed some warchiefs prior to the clip above—the massacre is mostly bodyguards and captains. Still, given the amount of planning this had to take, it's impressive to see happen—and indicative of the sorts of wild things you can do in Mordor, with a little patience.
So, how'd they do it? They explain in a comment on Reddit:
Among the last tier is an ability called dispatch, it kills all your controlled Uruks in your vicinity.
I spend hours getting every captain to level 20, sending them a death threats and making them bodyguards of my Warchief.
After summoning my Warchief I used dispatch to kill all of them at once 24 in total.
Dispatch, for those that don't know, takes advantage of a player's branded orcs. Branded orcs are orcs that fight for you. In any case, Schreckstoff explains further:
Among other things, after dominating [your orcs] you can keep sending them on missions, which I used to recruit other captains, sending a death threat raises the level by 5 and making them bodyguards does raise the level as well.
Afterwards you can just keep advancing time to level them, but that method is the most cumbersome and should only be used once you have all captains under your control.
I kind of want to see what sorts of ridiculous situations I can stage through dispatch and branding now, too.