A rancor/oversoul system for monsters?

http://imageshack.com/a/img924/998/C3mNru.jpg

Rancor

The land seeped in aether the souls of the slain linger still; converging on their kith and kin to share their rancor.

Oversoul

Once claimed an enemy will check your or your party/alliance number of kills of it's species or allies and apply the Oversoul buff if you meet the threshold. In the case of groups it will be determined by the highest number any one player has within the group. Rancor degrades over time or is reset by hitting maximum rancor and triggering an oversoul limit. Maybe some other method like an alchemical potion?

Oversoul could:

• Increase an enemy's stats.

• unlock new deadlier moves.

• Increase exp gain.

• Increase spirit bond gain.

• Unlock new/more loot.

• Unlock the area leash allowing oversoul mobs to pursue player characters for longer.

Rancor Aggro

Rancor enabled enemies could have a more in-depth aggro system with rancor checks and claims being made upon aggro instead of upon hit(to prevent over-soul buff missuse).

Oversoul Limit

Once rancor has been built to maximum; many things could happen:

• Oversoul Limit Breaks: Tonberry casts Everyone's Grudge- Powerful potentially party wiping moves with maybe some extra impactful debuffs like 15 minutes weakness should you die.

• Claimed NM Spawns: Tonberry King won't rest till your dead!

• Fate Spawns: The Tonberries are so peeved they decided to vent their frustartion on a poor little backwater village.

• Unlock an Obstacle in your path: Incensed the Tonberries open the gate to pursue you.

• You receive an offering: You open the casket of loot and find a note; "please stop killing us Tonberries.=("

UI/Display
To properly communicate all of this SE could have:

• Log messages describing the increase of hatred towards you

• Rancor list in the menu listing all the species rancor levels

• Monster HP Bar color change

• Oversoul Animation/Skin

• Enemy's increasing in size upon aggro.

I had this idea while thinking about how to implement some more depth into the open world like NMs etc without reducing accessibility of the zones. But really SE could use a system like this in just about any kind of content. Now that i think about it FFXI had a similar more simplified system everyone knew as Fomor/Tonberry hate.

I feel like this would be pretty neat for certain world zones meant to make some use of it, but would rather not see, say, a former WP-speedrunner unlock 4 more Tonberry King skills upon an unwitting party of new players.