The Infernal Grendels occupy Grendel slot V and were created using Geneforge/Eggforge/Gimp.

They come complete with a modified CFE Grendel genome that see them more resistant to many types of poison and injury, as well as increased aggression and resistance to heat.

Before hatching your fiendish new friends you will need to install the bigger sprite allocation fix by Verm, otherwise your game will crash when they reach adulthood.

https://creatures.wiki/Bigger_Sprite_Allocation