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Is the genestealer cult legal? and if so were can i find the rules?
The only 'legal' way to play a genestealer cult is to use Imperial Guard or, better still, Lost and the Damned rules.
However, there are plenty of rules on the internet, so if you don't mind having to ask your opponents permission, you could use those.
And in the future, please bother to read at least the most newest topics... Genestealer Cults was posted just a day before Yours. Avoid multiple posts on the same topic whenever You can, thank You! (Y)
"The meat things seek to destroy ourselves. They hunt us as we hunt them but they are weak and uncertain. The inferior flesh will be entirely destroyed, all biomatter consumed. Ourselves will fight to the last, all weak flesh must be devoured."