Who says that only humans can be part of your Necromunda gang? Nobody, that's who. If you want a trained alien-gator, you can have a trained alien-gator. At least, soon you can have a trained alien-gator. Forge World is taking orders for the Goliath Sumpkroc now over in their webshop.
From the website:
Hive legend has it that many thousands of years ago, during a different age of Necromunda, a now long-extinct type of reptile became the fashion accessory of choice for uphive nobility. Today, the Sumpkrocs that House Goliath keep are somewhat different to the original creature, with centuries of genetic cloning causing a few changes and they no longer wholly resemble the creature first imported…
Add an Exotic beast to your Goliath gangs in games of Necromunda – a strange and wonderful beast loyal to its owner, with its own unique stats and skills – with this multipart resin kit. Goliath Sumpkroc is a bountifully fanged Sumpkroc, a hardy beast of muscle and tooth. He comes as 6 components, and is supplied with a 40mm Necromunda base.
Rules for fielding Sumpkrocs as Exotic Beasts can be found in Gang War 3.