I like that a lot, kind of like what LCS said combined with the snake thing, so long as it has a sort of bellysack/cage, essentially something the opposite of a tervigon that sort of just grabbs people and stuffs them into some sort of incapacitating storage tank, something with really high initiative, MC with high toughness, and maybe some sort of shrouding/cloaking device+lictor style rules. and then to make it a real weird one, the ability to recover "trapped" models once the thing is destroyed.
Maybe some sort of intiative test to avoid being captured so itd be proper that characters/high initiative units could avoid being grabbed but the thing would tear through yr average Militarum/Tau/Ork troops choice easily
im envisioning sort of a gangly brass scorpion with a fat butt