Below is the official answer for adrenal genestealer.  However, just want to clarify further.  If the marine didn't die for a 0 die roll because of artifact card or any other reason, does the swarm contain the adrenal genesteader shift or move?  Many people think they move, but it clearly says they should shift.  I believe shift meaning if the swarm is in the bottom half or exactly middle of the formation regardless left or right side, the swarm goes down; vice versa, if the swarm is in the top half of the formation regardless left or right side, the swarm goes up.  All other swarms stay in the same place, even if there is a swarm engaged with the same marine on the other side. 

Am I correct?  Please clarify.

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"What happens to Adrenal genestealers if a 0 is rolled on defense but the space marine is not slain (e.g. a support token is spent to reroll, or a special ability is invoked). Does the swarm containing the adrenal genestealer attack again? Does it attack the same space marine, or does it shift? (As the icon on the card would suggest.)

If a support token is spent to force the defense die to be rerolled, the original roll, in this case "0," is ignored. For any other reason the attack was not ignored, and the Space Marine survives the attack, the Adrenal Genestealer and the formation it is in shifts and then attacks again.

Andrew Meredith"

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