The Duke mission, "Make It Slow", states that the objective is to "Defeat (playername) after X turns in a single attack". This makes it sound like the player needs to score a one hit kill after X turns have passed, which can be extremely difficult to do since you need to attack each turn and risk dealing damage. However, the actual objective is just to defeat the player after at least X turns have passed, which is much simpler to do.
For me, it was "Defeat superyoshi64 after 7 turns in a single attack".
I'm not sure if this classifies as a bug or if I'm just somehow misinterpreting the word "attack" in this case, but I figured I'd post it here just in case.