Thunder555 wrote:1. Tyranid warrior with rending claws and toxin sac. Since it would be a same "weapon" with both characteristics, they don't need to choose which ability to use in close combat. Yes or no?
Toxin sacs are not a weapon for Tyranids. Regardless of the argument about weapons stacking, you'll be fine with rending claws and toxin sacs.
Thunder555 wrote:2. New carnifexes can't have Heavy Venom Cannon and Stranglethorn Cannon at same time. Yes or no?
They can only take one of those options.