First of all make a tower of blocks in the sky so the flame thrower can shoot down at mobs and/or players. In the sky put five dispensers side by side face where you want it to shoot. Next hold shift and place redstone dust on top. at the back of the middle dispenser place 3 block going behind it. behind the block make a 2 by 2 square and on top plack a comparater and a lever on front of it where the two red stick of pointing up. Place redstone coneting it all up and fill all the dispensers with fire charges, the more the long it lasts before you have to re fill it. make sure you click the comparater once so it works right. Now click the leaver and mini fire balls will fly out set mobs and wood on fire. If you fill up all the dispeners the fire can go on for a very long time(like a hundreds of blocks) and if your the target of the flame thrower the first thing you will see is a huge storm of fire (literally) before it burns you down. This can also work on bedrock as well so mobile/consle players can enjoy the fun too!