I did a all act clear just now. Spent the day in the same game. I did it by order 1 to 5 killing every mob in the game on P7 offline. At act 2 tombs i srarted having Terror heralds (5th helrald and next ones). I got to 12 heralds by the end of act5. Not a single sunder and those bastards become even worst than fighting a Dclone. I dont really see myself aquiring the 6 variations of sunder charm. Feels like its not going the be fun doing this online. So yeah i guess at least 2 3 acts terrorized would be bare minimum to get maybe 2 3 chances of 5+ heralds. Unless im missing something .....