Parasite Pack

From the first screen after starting the game, jump on the cloud to the left, and then up to the cloud to the right of it. May take a few tries, but you can get on there. From that cloud, jump all the way to the left, and you will get kinda "stuck" on the sky, and then go onto a different screen. Low jump under the white and red things that kill you by mashing , then go down the hole on the left.

You will see numbers above more holes. Keep going right before falling down the hole between 31 and 35, then falling down the hole to the right. Here, your achievement should pop.

Once it has, you can hold the to rewind back to the area with the numbers to unlock more achievements.