Rules for Mind Worm are on Ezekiel's summary page. It's in this thread already.
It's basically S4 AP2, D3 shots at 12" and anything that takes an unsaved wound from it loses a bucket of stats--3 Ld, I, WS, and BS.
But like any and all "lose stats on unsaved wound" abilities, you'll almost never see it matter, as 99% of things only have one wound and the few that don't will generally fall into one of a couple categories:
A). Things your Librarian has no business being within 12" of
B). Things with wacky defensive capabilities preventing that S4 AP2 shot(s) from having a serious chance of landing
C). Things with a dozen guys willing to Look Out Sir the shot, even if you happen to pass the Focused Witchfire threshold to allocate it
What I'm saying is, ignore the stats-altering part of it, because you might see it affect a game in a meaningful way if you start playing 40k right this second and continue doing so for the next hundred consecutive years.
So basically, Ezekiel is forced to spend one of his 3 Mastery Levels on a 12" D3-shot S4 AP2 weapon. Meh.>captcha: inasmuch pop italy