To get this achievement you must alter the game rules so it plays like the first game (Nidhogg).

The first thing you want to do is open a local match (or online match with a friend). In the character customisation screen press ENTER on the keyboard or the MENU button on an Xbox controller to set the game rules.

From there you should set the time limit to NONE.
After that, select the WEAPONS menu and deselect all weapons aside from the rapier (thin sword). This is becasue it was the only weapon type avaliable in the original game.
Go back to the SET RULES menu and choose CHEATS, make sure that you have 'NO SLIDEKICKS' on and all of the other cheats off.
Finally, play the match and you should automatically get the achievement.