The Maw

The first time that Maw receives the Gastro power is in level 1 ‘Crash Site’. Maw has to grow twice before he is large enough to be able to eat a Gastro; you can do this by eating some of the Yums that appear in the same area. To get the power, you have to attach the wrist device to a Gastro by pressing B, and either throw it (hold Y to swing; let go of Y to throw) or drag it into the water to get rid of its flames. It is now safe for Maw to eat it.

You can flame most types of vegetation and living creatures with this power just by walking up to them. Unfortunately I wasn’t able to get this achievement on my first playthrough of level 1 because Maw would quite often eat the yums before he flamed them. However, you also get this power in level 3 ‘Chaindown’ and there are more than enough objects between the two levels to get the 150 needed. The power is also available in the Brute Force and River Redirect DLC levels. You can also replay levels and your progress will carry over, so playing level 1 twice would provide more than enough objects for you to unlock this achievement.