Nevermind, it's actually when you have:
- Backtrack
- Very low spell cooldown
- Very fast mana regeneration
At that point, because I can spam backtrack I can spam other spells too. And because of the mana regeneration, I can do this indefinitely.
I was literally just spamming 1, 2, 3 and 4 as fast as I could while spinning around and didn't even see a single enemy for the entire round because I was just instantly killing everything.