Welcome to The Modding Screwups Thread - this is where you, the enterprising modder, can share stories about the terrible and wonderful anomalies that have appeared when you were modding. From the bizarre effects from duplicated raws to the amusing misbehaviour of a misplaced 0, you can share your stories here!
Additionally, if you still have the raws that cause your upsetting/hilarious behaviour, upload them and let people play around with your wonderfully broken worlds.
Here's one from some time ago:
The Bursts
I had decided to make an animal created solely for fortress defense. As a sort of mobile landmine, I decided to give the creature boiling hot gases for blood, and in playing with the new (at the time) syndromes I added some debilitating necrosis effects from the blood-gas. I named these little critters "bursts", and they were tameable, trainable little pets. Which is where I went wrong. I only noticed the error of my ways when migrants started turning up with their own pet Bursts, and rather unfortunately one of them got into my danger room and, well, burst. So the burning hot poison gases spray around the room, quickly setting off another Burst in the doorway, and then another down the hall - right next to my kennels. Fortunately, the kennels didn't erupt and I thought I was safe - but, of course, the owner of the first stricken pet decided right there and then to have a tantrum and planted a kick firmly into a Burst, sending it flying backwards into the wall of the kennels, where it exploded - all the other Bursts following shortly after, filling the Kennels with the poisonous, burning muck. It wasn't long before most of the fortress was ill and dying, and then the goblins invaded and finished them off.