Vanquishing my Lich holding a Kuva Brakk. This was the fastest one I've done, taking only a few hours -- I was very lucky though, my first rune was in the first slot, the second was in the second slot and third was in the third slot.

The Lich only got up to Rank 2

Though it glitched during the fight, and I never got the first rune sequence (the "placeholder" animation played instead) and the final rune sequence was skipped entirely.