My 2 cents to not destroy Vel Koz after his rework: New Passive - Analyze them

Since seems like Riot is going to rework Vel to give him "a unique identity that makes people pick him over other Champions" I thought of this.

Passive:

• Same as his old passive, maybe with a bit less true damage with the 3 stacks?
• New: Analyze Them: Every time Vel Koz kills a Champion, he gains a permanent buff against that particular Champion (damage? Defense? something else?)

This would give Vel an identity on why people would pick him over Xerath for example: you trust you are going to kill your enemies and snowball.