Many thought it was madness, foolish even. Others considered it inconsiderate of those lost to the invasions. Yet despite these oppositions, some Rogue Traders have gone about modifying captured tyranid bioforms. Retaining their incredible abilities from their respective Hive Fleets, while some gave them more 'appropriate' forms for various unknown reasons. Whoever started this long chain of heretical experiments, nobody knows. Only that it has gotten so out of hand among parts of the Rogue Traders that the Inquisition gave up trying to track each one down. Merely punishing any dumb enough to reveal any in their acquisition

You yourself were among one of those many traders, admittedly it was difficult given acquiring bioforms for such efforts requires great effort. Especially those of the one you sought, those of the sinister trygons. But after countless attempts, and many more after with the process to make it successful, you had done it.

(Modified heavily after input from a friend on Discord)