I am Mindslave

Since they have lowered the Par Score requirements this achievement can easily be done on normal difficulty with 0 skulls. Take the tank at the start of the mission and kill every ghost, wraith, and banshee on the way to the tunnel as well as shooting the turrets on the phantoms as they fly by if possible. If you do all of this, you will already be at or past the par score. From here, just play as normal and if you minimize your deaths, you will complete the level with the "Ripple Fire" achievement in the bag. I would recommend not taking too long in the tunnel because if you go over par time, you start losing score.