Pacify Farm Secret Ending Guide

To get the secret ending in Farm, you have to complete the level as normal. After you feed the monster 9 poisoned chickens and it passes out, instead of bringing it to the van, you will bring it to the graveyard next to the box where its body will vanish.

After that, bring a poisoned chicken next to the box where the monster's body disappeared and interact with the box using the poisoned chicken. This will spawn a giant green chicken which will run to the front of the farm. You can then kill it by hitting it with the frying pan until its health runs out.