Everytime you put a certain mob drop and an axe into a smithing table, you will get the axe, but with an enchant added to it.

Blaze Powder & Axe = Axe with FireAspect X, whenever you hit player, they get on fire.
Bone & Axe = Axe that give damaged player blindness and makes it so that the player cannot jump for 5 seconds.
Gunpowder & Axe = Axe that triggers explosion that ONLY HARMS DAMAGED ENTITY.
SpiderEye & Axe = Axe that gives damaged player Poison and Nausea RottenFlesh & Axe = Axe that gives damaged player hunger and slowness GhastTear & Axe = Axe with knockback 10, and also gives damaged player levitation
Enderpearl & Axe = Axe that teleports damaged player anywhere near where they were before, when i say near, i mean only 10 to 20 blocks, also, players could get teleported into walls and suffocate.