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The tourney is annihilate rules with the standard force organization. Is there any specific nids that are must haves in small point games?
1 Tyranid Prime for your HQ and a unit of 3 or 4 Warriors in smaller games. But that's about it.
Hive Guard are a steal at low points and do a good deal of damage. A Tervigon with catalyst is incredibly mean as well.
My 500 point list for a local campaign was:
Tervigon - Catalyst
x14 Termagants - Toxin
x15 Termagants - Toxin
Reason for Toxin on the gants rather than the Tervigon is that the Tervigon is never in the 6" bubble to help them out.
Hockeyman's got it nailed, Tervigon and hive guard, job done really. Then just add hormaguntas or something and away you go.
As for warriors, not a great idea, admitedly theres a lot less that will ID them in such a low points game, but they'll be a prioritory threat and would never make it over the table.
Your friendly neighbourhood gargantuan creature