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I was wondering if you had a brood of three tyrant guard in cover with a hive tyrant armed with range weapons outisde of cover and they got shot at by AP2 weapons could the tyrant guard go to ground giving the unit a 3+ cover save but also since MCs cant "go to ground" could the hive tyrant still shoot next turn because only its "retinue has gone to ground and not the actual MC.
The normal tendency of the rules is that if even 1 model in a unit has a limitation, then the whole unit is also limited by that 1 model (unless it explicitly says otherwise).
Example - units are limited and move at the speed of its slowest member.
Broodlord + Genestealers - because broodlord doesn't have fleet, his retinue cannot fleet.
Terminators + IC in non-terminator armor - because the IC cannot Deep Strike, so neither can the Terminators if he is with them.
Thus, because the Hive Tyrant cannot go to ground, then neither can his Tyrant Guards.
The unit can go to ground (Living Fortress in Apoc:Reloaded pg 41 has a special rule about when the unit goes to ground, but doesn't make a special allowance saying that the unit can go to ground if it normally couldn't so I'm assume a HT with T-guard can go to ground), but I don't think the tyrant can shoot and the tyrant wouldn't get the improved cover save (though he would still count as being in cover as the majority of his unit is in cover).
Or at least thats how I would play it.
40K armies: Tyranids (2001), Space Wolves (2008), Sisters of Battle (2011)
Current Rep: 1337
thanks for the input guys, i guess I'll just have to stick with the 4+ cover save