ULTIMATE leo129

*requires you and your partner to have Arena DLC*
*recommend for higher level characters to do this. My partner and I did this at level 51*

Go to Arena A (easy difficulty) and kill everyone until wave 4. By wave 4, the infected start spawning. Have your partner cautiously kill all the Walkers and whenever an infected chases your partner, have him lead the infected to you, and that's when you kill him. Repeat this four more times. Make sure you do NOT kill any Walkers in between your streak. If a Walker comes towards you, run away! Let your partner take care of it.

Best way to do this, especially if you own modded rifles that do 1-hit-ko damage, is to camp at the entrance of Arena C (Hard difficulty). They spawn in the NW and NE corners so focus your attention there.

Best way to do this, especially if you own modded rifles that do 1-hit-ko damage, is to camp at the entrance of Arena C (Hard difficulty). They spawn in the NW and NE corners so focus your attention there.

Here are two videos, one that is the walkthrough of the main part and the other is the boss. although you may be thinking its a moth, this isn't the moth that gives you the achievement.
https://www.youtube.com/watch?feature=player_embedded

This is "complete mission 3" worth 10G
In this mission you will be chased by a giant worm. There are two rocket launchers. Take them and save them for the end or use them on the worm. and if you have time and the patience you can kill it. FYI: It will respawn but you don't have to re-kill it. There will be no waypoints during the chase. Once you reach the abandoned warehouse you will get a waypoint and face a boss. Take the VS suit and shoot both weapons until you are forced to eject. There is a VS suit rocket launcher around the battle field. Take it and use all the ammo on the boss. If/when you lose your ammo, use the rocket launcher ammo I told you about in the worm chase and use the rest of that ammo on the boss. when defeated you will either get "10G mission 3 cleared" or if killed the worm, like me you will get "2 for 60G" meaning 10G for mission 3 cleared and 50G worm hunter.

This is gonna basically be identical to SkillfulMmd's solution, but I know some people like me perfer to see it on videos, so here is a video. If you understand the location that SkillMmd was talking about, skip to 4:00. if you don't, just watch the full thing.
http://www.youtube.com/watch?v=5AtJ7S8s04k