The following questions are lifted directly from GW's Tyranid FAQ. The answers have been substituted with my own.
Q: If I have more than one Hive Tyrant with the Hive Commander ability, do their bonuses to reserve rolls stack?
A: Yes. “Whilst the Hive Tyrant is alive, you add +1 to your reserve rolls” (Codex: Tyranids, 34). The semantics are clear; if the ability were to not stack, it would have to say something like “Whilst there is a Hive Tyrant with this ability alive…”. But no, whilst the Tyrant is alive, you add +1. A second one also alive? You add +1 for that one too.
Q (Cont’d): Also, do I get to outflank with one Troops unit, or one Troops unit per Hive Tyrant with this upgrade?
A: This one’s less clear, and could very well go the way GW decided, so I’m not going to whine about it.
Q: If a Tyranid unit takes a Mycetic Spore, can an Independent Character join the brood before deployment (and hence deep strike in with the brood)?
A: This one, I don’t know about. On the one hand, the rules for reserves indicate that for those purposes, an Independent Character that joins a unit is considered part of that unit (so for the duration of its transportation, the combined unit would qualify as a single one, BBB, 94) and the closest rules we have, being those for transport vehicles, similarly allow Independent Characters to join units being transported (BBB, 67).
However, for general purposes, the Independent Character does not explicitly count as part of the unit, but merely moves with it (BBB, 48).
I would have allowed this, but I’m afraid this really is a grey area.
Q: Does Shadow in the Warp affect psykers who are taking a Psychic test whilst embarked within a transport vehicle?
A: Why. On. Earth. Wouldn’t it? I’ll quote you the transport rules (from BBB, 66): “If the players need to measure a range involving the embarked unit (except for its shooting), this range is measured to or from the vehicle’s hull.” Clear as crystal. There are no inherent immunities from being inside a vehicle except (implicitly) from shooting. Other similar powers (like the Eldar Farseers Runes of psyker botherance) have no similar limitations. Why the heck would the all-encompassing Shadow in the Warp not affect a psyker just because he’s inside a tin can?
Deep breath. Calm and easy.
Q: Do Lash Whips affect Sweeping Advances?
A: I know this one is shaky, but I’m going to argue yes. See, the Lash Whip says: “counts their Initiative as 1 until the end of the assault phase” (Codex: Tyranids, 83). I also feel a sense of corroboration from a later entry in the Tyranid FAQ, which says that it is the new Initiative of 1 that is modified by things such as Furious Charge. Surely, if the Lash Whips were just another modification, the order would have been less clear?
So there you have it: my whining about GW's understanding of their own rules. Sorry if I got a bit riled up...
'Til next time.