The Fold WeaponWeapon:
At the beginning of the mission, you'll be given the smart pistol, and can easily attain this in the first hallway afterward; but there are many opportunities throughout the missions.
Just find a group of enemies, start a slide while the gun auto locks-on and then shoot when at least 3 enemies are marked. The achievement will unlock when they are killed.
The same strategy can be used for:
The I know Kung Fu achievement in Titanfall 2 worth 26 pointsShoot and kill 3 enemies in a row while wallrunning as a Pilot in the Campaign