Minecraft

Ghasts are located in the nether. They are giant white cubes that fly around and shoot fireballs at you. For this achievement, you have to hit one of these fireballs back at the ghast AND kill it. This can be difficult in the large and open spaces of the nether, so if you can, try and lure a ghast to a place with a lower ceiling.

This is a link to a playthrough of multiple attempts trying to get this achievement. I finally did it. I tried a lot longer than 18 minutes but fortunately I caught it on video. It's a harder achievement but if you have the difficultly on easy, and wear some fire resistant armour, or take some fire resistance potions, you'll be golden.