For this achievement you have to kill 1,000 of any
Animal NPC. I chose to do this in Singleplayer.
Load up any map, hold Q, select NPCs, then Animals.
The four Animal NPCs are as follows:
- Crow
- Father Grigori
- Pigeon
- Seagull
I chose the pigeons and spawned a ton in one area of the map I was using. If you don't have a decent PC I don't suggest spawning in too many. My frames dropped from 60 to 7 after having around 500+ pigeons on the ground.
After you have a horde of pigeons, hold q again and spawn yourself some explosive weapons. Now get to a safe distance and start massacring the poor birds. After spawning and killing 1,000 you will unlock this achievement as well as:
Here is a video I took in case you need visual reference: