Poison rats?

[Thaliel]

How do you get these?
I can only find toxic rats in the library

[JinxVIII]

If you're asking about the rat that is colored orange and purple, it's a hybrid rat called a Poison Rat--the other hybrid being called Toxic Candy. You can breed for it with Orange and Purple Toxic Rats.

The journal has a complete list of the hybrid outcomes : )