From NS2 community wiki
Frenzy is an upgrade from the offensive Whip structure. Frenzy heals the player after a kill with the amount of extra damage done, for at least 10 health.
- Frenzy: On kill, get health back equal to extra damage done; health comes back over time (approx. 15/sec). Frenzy scales reasonably for Skulk to Onos, and extra damage upgrades and group tactics can increase the benefits.