This achievement is particularly harder to get than other achievements since the Yeti Boss is one of the hardest bosses to defeat in Garden Ops, due to his speed, making him hard to hit, and his ice-based attacks that can freeze you very quickly. A good strategy would be to stick to any Sunflowers on the team, or plant Heal Flowers if there aren't any. Make sure you get the final hit on him, or else you will not get this achievement.