For each Interval/Score achievement you will need to maximize your points gain. This is easier without a partner as your individual score is needed to earn this achievement. This Interval is by far the easiest to earn the required points on and there's not much to it. Be sure to grab the Alma Doll and the one Psychic Link in the level. When you enter the Gym, repeated melee the punching bag to earn the "Yo, Adrian!" achievement if you haven't already. Now continue on until you reach the Creep. The Creep's weakpoint is the glowing spot in his mouth. Every time you damage the creep you earn points and even more points if you can damage him without him hurting you. Be sure to kill his Ghost Soldiers with cover, slow motion and headshots. If you neglect damaging the Creep, he'll continuously spawn Ghost Soldiers in for you to work on other challenges (though you'll miss out on the Creep Damage challenges).