The release details are here, and there will be a single box set release for Tyranids that can build either the Maleceptor or the Toxicrene. Get out your respirators, your going to need them........
Please remember that although these are from an excellent source, all early information like this must be considered rumors.
via a solid source on Faeit 212
Tyranid Toxiccrene/Maleceptor 1 miniature $73
Warhammer 40k: The Rules small format hardback $58
Tyranid Dice Tin 10dice $17
On a large oval base with 10 long tentacles and a face like a lictor.
A 5 wound t6 monstrous creature who is hypertoxic and shrouded. this means any hit gains instant death on a wound roll of a 6 due to a toxic cloud. This includes its close combat attacks and its choking cloud
Choking Cloud; 12" assault1 ignores cover, lg blast. Chocking cloud is S3, poisoned 2+ and against open topped vehicles or any vehicle that has lost a hull point the attack gains armour bane.
A 4 legged beast with two large scything talons
A psyker level 2, synapse monstrous creature that has an invul save of 5+. It has shadows of the warp and a 4+ save.
It has the psychic power psychic overload, which is a 24" focused witchfire. target must take a leadership test on 3d6 and vehicles count as leadership 10, failure causes d3 wounds no armor or cover saves allowed, and a causes a single glancing hit to vehicles, no cover save allowed. The maleceptor can do psychic overload three times a round, but cannot target the same model twice.
It can choose its remaining powers from the powers of the hive mind.