The Maw

To unlock this achievement, you need to find all 7 snuffles located within the game. Since I had a hard time finding them, I thought I'd share the locations as I found them in-game.

Level 1
After you learn how to move rocks using the B button, you will find another rock blocking a path to your first snuffle. This path is located further to the left of the waterfall near the exit in the final zone. Move the rock and continue up the path and you'll be able to devour it with Maw.

Level 2
As soon as you start the level, turn around. You will see a rock that you can move. Behind it, you will see a snuffle within a crate. After you obtain the Bulbous power, use it to electrocute a slug and throw one of those bad boys onto the crate. Once this is done, you will have your second snuffle.

Level 3
Once you obtain the Gastro power, burn the Venus Fly Trap plants and your third snuffle will be behind them.

Level 4
After the first vent, you'll eventually find your way to a group of islands full of more vents. Simply jump and float using the vents to land on an island containing a snuffle. Once you're on the island, smash the crate containing snuffle by jumping and pressing X. Snuffle will then be free for Maw to eat.

Level 5
Once you obtain the Loofer power, you will see an open area full of space ship parts. You can destroy these parts with lazers while you're aboard Maw. Destroy all of the space ship parts (it will help you unlock an unrelated achievement) and you'll find one space ship wreckage blocking a path. Use your lazers to open the pathway and you'll find your fifth snuffle through the passage. Use your lazers once more to break open the crate and enable Maw to eat the snuffle.

Level 6
Once you get the Puff-Tor power, look for a rock near the Electric Fruit field where the Bulbous collect. Using your Puff-Tor power, smash the rock to reveal a vent. Jump and float towards the vent to have it float you up to the cage containing the sixth snuffle.

Level 7
Once you obtain the Beetull's power, look for a snuffle sitting on a table-shaped rock. While using the Beetull's power, knock the seventh snuffle off the rock. Once you eat this final snuffle, this achievement is yours!