Minecraft wiki entry for Defeating_a_Nether_fortress, associated text: They spawn from spawners. Kill them with fire resistance if you can get the potion/totem of undying. Their ranged attacks will have no effect if you have fire resistance. It is possible to kill a blaze without fire resistance. Shoot it with a bow, or knock it back with a sword. Blazes don't take fall damage, but snow and water can damage them.