On this page of the game guide to Borderlands 2 you will find a detailed description of the side mission titled Mighty Morphin. You can start this quest in the Sanctuary location after completing the main mission named A Dam Fine Rescue.
2) Varkid nests/mounds
Speak with Hammerlock  and take the Evolutionary injector. Afterwards head to Tundra Express and approach one of the Varkid nests/mounds . Shoot the bugs to reduce their life to around 30%. You don't want to kill them, so choose a weaker weapon. Larval Varkids should enclose themselves in a cocoon, as shown in the above screenshot. Quickly approach the cocoon and press Use (by default E).
The Varkid will then transform itself into a Mutated Badass Varkid. Kill it and take the Mutated Varkid Sample from its corpse. Hammerlock will then ask you to collect four more Varkid Samples. Repeat the whole process again - reduce a Larval Varkid's health to around 30%, use the Injector on the cocoon, kill the enemy, take the sample. After you collect enough samples, return to Hammerlock in Sanctuary  to end the mission.