I seem to occasionally get the "killed X creatures with one blow" bonus, even though I decidedly did not kill X creatures with a single shot. It sometimes happened to me when using "channeled" skills (such as rapid fire) and sometimes even using multiple regular attacks.
What is the exact condition for receiving the bonus? And if it's really "X creatures killed under Y seconds", then what is Y?
From my experience so far, you get Mighty Blow if you kill 6 or more enemies under X seconds.
I have not scientifically measured it, but I think the X is between 0.5 and 1.
It seems completely independent as to the source of the kill - a single skill activation, a channelled skill activation, multiple hits, traps - as long as it's >6 kills in <X seconds, you get the Mighty Blow bonus.
From what I have observed, you receive the bonus as long as you keep doing actions that kills enemies without interruption (to move, for example).
Clicking on another creature to go and bash it is ok, but clicking on the ground to reposition yourself is not.
You may think your multiple attacks were counted as one blow but they weren't. The only thing that could make it seem that way to you is the window of time between the end of the blow and the toast message that pops up on the screen.
There is enough time to attack a few times in there and it can look like it counted multiple attacks but it didn't.
One blow is 1 attack (even if that attack kills enemies at different times for whatever reason) or 1 continuous channel. Anything else simply looks like it counted multiple attacks when it actually didn't.
