That has to be the most frustrating mission of any game I've played in recent memory. You'll have to kill a total of five mutated varkids to complete the mission. Just jump into a varkid nest and injure but don't kill them. They will eventually go into a pod to transform into badass varkids. Hit square to inject the pod and turn them into mutated varkids. The only problem is Mordecai keeps shooting the pods before you can inject them. I raged so much on that mission. I had to have someone jump in my game and help me. Another important price of advice is to never inject more than one pod at once. Those mutated varkids will destroy you. I lost so much money on that mission due to constant deaths.