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Simple question:- Does the Impaler Canon ignore the cover save given to turbo-boosting bikers?
No it doesnt, the Hive guards rules say that the vehicle "can only count the benefits of cover if.... in or touching it" Note this is not saying it ignores cover saves, just that you cant claim a cover save under certan circumstances. Scince the bikers already have a cover save and are not tring to claim one for being hidden from LOS, the save can be taken.
Your friendly neighbourhood gargantuan creature
Basically, the impaler cannon does not ignore cover for special rules such as disruption pods, skimmers moving flat-out, smoke launchers or turbo-boosting bikes. It only ignore cover concerning actual terrain that gives cover relative to LOS or area terrain.
Record: Win - Loss - Draw: Hive Fleet Pandora (New) 32-6-6 Space Wolf 7th Co. 52-11-6
Blood Angels 12-4-2 Daemonhunters 20-8-3
Imperial Guards 12-5-2 Daemons 8-3-2