It was a group of around 10.
They used mostly Immob Rangers + Burn Guards.
They hid among their own mega blob first.
And when both sides started to engaged, they went group invis and attacked the enemy blob's rear.
Rangers dropped their immobs and Guards dropped their burning swords.
It was so effective at trapping large groups of pugs on a mega blob's tail.
And they repeatedly did it chunking down a mega blob section by section.
I didn't see the guild tag clearly because of all the lag/blobs but I think it might have been Eins or Brrr.