Null iron is known for being effective against magic. Null iron can only be found in cold temperatures, so only snow biomes will have it. Once in the snow, it is as rare as diamond. Null iron swords have 800 durability and plus +6 damage. It can be used in place of flint to make arrows (you only need one ingot for every 20 arrows in this case). However, what makes this worth having is that many creatures take extra damage from null iron, especially pixies and the like.