Highly Notorious Monsters

[Alerith]

How about an Oversoul system ala FFX?

Each time you kill a certain mob (Say a...Sphene Doblyn), you get a point towards a soul counter. This counter could be a tab in your attributes.

After you've killed a certain number of them (Say...100), an NM of that type of mob spawns. (Oversoul Doblyn)

The Oversoul'd NM would be a bit harder and have some better drops. Maybe a good yield for HQ crafting materials from lower-end mobs.

Now, what about Oversouling NMs?

Say you defeat Great Buffalo 10 times. After it's 10th defeat (at your hands), the Oversoul Buffalo would spawn. A bit tougher, better drops, etc.

And then Oversoul'd Primals.

Defeat Ifrit 10 times, the 11th time you enter the Bowl of Flames (Hard), you fight Oversoul Ifrit. MUAHAHAHAH. Blue flames! Multiple Inferno uses! AHAHAHAHA! Firaga!

Reward: Choice of Ifrit Weapon...... or grade 5 dark matter.

...*ahem*

But yea. Something akin to that.