Hey Guys,
today I will show you, how to make a FIRE STAFF in Vanilla Minecraft.
These are the Commands:

TESTING FOR ITEM:
/testfor @p {SelectedItem:{id:minecraft:stick}}

SUMMON FIREBALL:
/execute @p ~ ~ ~ /summon Fireball ~1 ~1 ~1 {ExplosionPower:5,direction: [0.0,0.0,0.0] }

You can replace the testfor STICK with every item you like to use, like BLAZE_ROD
Of cause you are allowed to use this :D