The level 100 Havoc skin is the first ever 3-stage evolving Legendary weapon skin.
As you get more kills (within the match), its eyes glow and its nostrils emit smoke, etc.
This was really fun to work on. It's the first reactive weapon skin that the weapons team has created at Respawn (unless you count the Pro Screen from R2)
Recommend ironsight for flexing during late game kill feeds, the smoke blasting and eyes glowing in ADS looks amazing.