For the past week, I attempted to get Spectral Fists Specialist, an achievement-quest in Halls of Torment. That and Lightning Strike Specialist took me more tries than usual.
For those two quests, I had to forgo selecting other abilities. In every other case previously, I took advantage of any tome or scroll I could get. So these quests indicate it is entirely possible to playthrough a level with only one ability.
The quest Spectral Fist Specialist was driving me crazy at some point. The criteria:
Hit 500 enemies for 25,000 damage or more. Overkill damage counts.
I was starting to doubt whether I had to hit a group of 500 enemies such that the damage sums to at least 25,000, or that I had to hit for 25,000 damage 500 individual enemies.
if (spell_damage * enemies_hit >= 25,000
and enemies_hit >= 500)
then complete quest;
or
if (spell_damage >= 25,000)
then eligible_hits +=1;
if (eligible_hits >= 500)
then complete quest;
It is the latter though. I triggered quest completion during a boss fight when there were sparse spawns.