During the Black Seed Scourge event, there will be a mission highlighted on Venus. You must complete the mission 3 times. In order to complete the mission you must capture both targets, unlike your regular captures where one is enough to complete it. Also, you must do this with only a melee weapon equipped. The game will tell you this if you attempt to do the mission with any other weapons.
Though I have not confirmed it, these should also count towards your
The The Sword Alone achievement in Warframe worth 84 pointsComplete 10 missions without any primary or secondary weapons equipped.
....AND don't forget to snap with your TA App for