Dimachaeron
A Dimachaeron is a new giant tyranid monstruos creature and is essentially the tyranid version of the Eversor assassin, with steroids. He appear indeed to have evolved only to slaughter those identified among their prey as leaders in the midst of battle, spreading terror and dismay among the ranks of all who resist the Hive Mind's advance. Contrary to the Lictor, whose approach is stealthy and slow, the Dimachaeron throws all subtlety out the window and relies only on brutality and animalistic rage to destroy anithing the hive mind wants dead.
On the Tabletop
The Dimachaeron is a murder machine. That's it. He has 5 attacks base (6 because he has two melee weapons) is WS 8, strenght 6 and initiative 6 and come equipped with Adrenal Glands and Rampage to make him even more frightening. Then there are his special rules and equipments: he is a leap mostruos creature and can chose to leap in the movement phase or in assault (The first works like jump infantry, but with only 6" range, the second gives him +1 S HoW with Strikedown) and he has two close combat weapon. The grasping talons are S+1 AP2 Talons that, when it rolls one or more 6 to-hit, gives an attack on an unwieldy S+4 AP1 ID claw that can kill anything smaller than Extremely Bulky, while the Sickle Claws are an AP2 pair of claws with 4+ ID, for when you really want to kill that bloodthirster. Furthermore, if you chose to use his grasping talons and kill one model with the thorax spine-maw he gain a number of plasm token equal to the model wounds and that goes away starting from the end of the following turn. Until he has at list one token he have the FNP (4+) special rule, meaning he can be a terrifying Distraction Carnifex! Keep in mind that he has istinctive behaviour (Feed) but that shouldn't be that big of a problem given that he's LD 10. He also isn't fast, even being a fast attack attack choice, and will attract a lot of fire for his ability to obliterate everything he bump into short of a few special characters, so consider to embark him in a Tyrannocite and drop him in the mist of the enemy army. It is a risky tactics, but your opponent will be quite hard pressed and will have to choose if he wants to concentrate fire and obliterate him immediately, letting the rest of your horde close on him, or let him live and see his army ripped in peaces the very next turn.