RESEARCH and DESTROY

Another spot you can farm this is when defending “The Sands” without a university built or when attacking “The Sands” for the first time. Until you push the objective when you first start the mission the game will only spawn zombies which you can easily herd into a group to make it easy for all of them to hit the launch pad.



Ignore the beginning I was trying to boost some other stuff too.

I did this one on Great Transylvania at threat level 2. You'll spawn on a bridge and after walking a few steps you'll be ambushed by ghosts and zombies. As soon as that happens, go back to a narrow passage on the right side of the bridge(left when you're retreating) wait until the zombies form some sort of line and put a propellor in front of the first one. If 5 of them get bounced by it on a single turn, You'll unlock it. Here's a video of me getting it: