Krinkle Krusher

Use a meat item or wait for a big wave of Krinkles that include at least one elemental like fire, wind, or mud. Use the corresponding elemental attack twice on the enemy to make them grow bigger. Kill the bigger elemental enemy to make him blow up and kill the others near him. If this blow kills 4 or more enemies, you get the achievement.

Below is a video showing you how to do this with a fire elemental:

I did this at level 10.
Wait for a big wave with fire Krinkle and use the food for regroup them all.
Use fire, then 3 bolts on the fire Krinkle, they will all exploded!