Marvel's Guardians of the Galaxy

The Eye of the Hurricane ability is Quill's third ability and costs three ability points to unlock. He jumps in the air and throws grenades all around him. They do moderate damage and heavy Stagger to all enemies around you. You need to kill a cumulative total of 20 enemies with the grenades themselves.

The grenades themselves will take around a third to a half of a regular enemy's health off, and obviously do much less damage to tougher enemies. As a result, the easiest way to get kills with this ability is to shoot up and weaken multiple enemies in a group (they tend to cluster together anyway) and then dash into them and quickly use the ability. The grenades should do plenty damage to kill at least three per usage.

​​​​​​​As with other combat achievements, you could grind this in a single combat encounter by using the ability and getting kills, then reloading your checkpoint to repeat until you unlock this achievement.