as this achievement has a little problem, i decided to write a note for this one.
achievement describes you need to knock down 50 penguins in Ice-berrrger that you should choose it from farm in free play or reach it in adventure mode. i tried some times and no achievement poped when i counted 50 pinguines.
then i found that you need to knock down 50 GREEN penguins as you see in the achievement's picture above.
Best way for doing this: keep your aimer at the top of the hill you seeing middle of the screen and just keep shooting. you will knock down 100 pinguins and the achievement will pop.
for this one i suggest regular controller.