The wrath igniter can be used to ignite blocks, much like a flint and steel. To ignite items, right click them. This creates wrathfire, which spreads quickly and deals high damage to any mobs that come in contact with it. Like normal fire, wrathfire can be stopped using water. It can only be used 5 times.
Wrathfire also changes certain blocks if it comes into contact with them. For example, grass blocks will change into regular dirt, sand will change into glass, glass will change into sand, stone will change into cobblestone, and cobblestone will change into stone.