You must start a new campaign and enable Modern Scoring for this to unlock!
This can be only be done after getting the grenade launcher. This can't be obtained until after finding the armory in the final chapter by saving all scientists. The weapon is then found in chapter 3 in the room with 3 crouched zombies right at the beginning.
When holding multiple weapons, use the D-pad to switch the one equipped.
- Load up level one after getting the grenade launcher.
- Proceed to the bridge.
- Save the guy from getting thrown off.
- Shoot a grenade into the middle of the bridge right after the scientist moves to kill 5 worms.
*If you miss it here, go a little further to the inside and shoot the monkey guy on the right.
Shoot the zombie on the stairs with a normal gun then switch to launcher.
At the top of the stairs there is a clustered group of worms you can more easily kill all at once. As soon as you crest the top.
If you haven't gotten it yet, this will also unlock