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. Interval 04 is a lot like Interval 02 but gives more people to kill and a few new weapons. The biggest challenge will be killing the Powered Armor with your basic weaponry. Use Shock Grenades to stun the Powered Armor and open up on him with frags and your G3. You can get 6 or more weapon challenges here (Strader, SMG, CAS, G3A3, Frag/Flash/Shock, Schuller). When you get your own Powered Armor be sure to kill 5 enemies with a melee or stomp and up to 20 enemies with exiting the Armor. At the end you'll fight against continuously spawning enemies; you can use this area to work on unfinished weapon challenges and to up your kill bonus.