Making mutations on "Mighty Morphin'" mission

You need to visit the Varkid Ranch. Shoot a few of the Varkids there and run around a bit, and eventually they will stop and stick their face in the dirt. At this point they will start to form a pod. A big orange sack thing.

Run up to it and press [E] to inject it. Then you can wait and a Badass Mutated Varkid will spawn, you can then kill that and that's it. Just repeat as many times as you need.

NOTE: a Varkid will not mutate into a pod if it's by itself

NOTE: (at least for the XBox 360) if you kill the mutated Varkid and the sample appears, make sure you pick it up. If you do not pick up the sample and save your game, then you will not be able to mutate Varkid in the future, so you will not be able to complete this optional side quest.

You only have to damage the varkids a little bit to get them to turn into pods, but sometimes you have to wait a few seconds for it to happen. It feels like forever. Then, as mentioned above, walk up to it and use your Use button on it.

If you've already woken up Mordecai, he might kill the pod while it's in the middle of mutating.