Grab & Slash
Background and rules for the short-lived Tyranid Grabber-Slasher assassin.

Background
White Dwarf 130 has a two-page short story about Inquisitor Kryptman investigating a living alien artefact. The story concludes in the next issue with Kryptman being hunted by a shapeshifting monster that consumes anything in its path.
He did not hear the approach of Death.
As he turned away, something catapulted over the parapet and smashed into the back of his neck, knocking him to the floor. Its warm body enveloped his head. The musky stench was disgusting. He dropped his lasgun and flung his arms up to his head trying to tear the creature away. Savage claws raked at his throat, ripping open his windpipe.
He tried to scream but all his horror and pain just came as a racking gurgle. His questing hands pulled at the thing, futilely trying to pull it off, but it was slippery with a corrosive fluid. Razor-sharp teeth flayed the skin from his fingers. The pain was terrible, building up inside him with no release. Fire seared through the back of his neck as claws cut deep through the top of his spine, cracking his vertebrae apart. Sensation flared and dimmed. The last thing he felt was something punching through his eye sockets.
-Inquisitor Kryptman by Lindsey D Le Doux Paton, White Dwarf 131, 1990
WD131 also included a preview of Advanced Space Crusade.
Advanced Space Crusade

GRABBER-SLASHERS
The Grabber-Slasher is a destructive warrior assassin which has certain biological traits in common with Orks, including blood containing symbiotic algae which enables the creature to digest its prey. Indeed, it is possible that the Grabber Slasher has been created from Ork captives, in which case it heralds the birth of new bio-constructs based upon creatures from the human galaxy. The algae in the Grabber-Slasher's bloodstream synthesises the genetic material of its victims which is then absorbed into the Grabber-Slasher's body enabling it to gradually mutate its own form. However, the Grabber-Slasher can always revert to its basic Grabber Slasher shape, although the change may take a day or so to complete.
Its powerful body is very muscular and it can propel itself along by its tail. A single flick of its tail sends it bounding through the air towards its chosen target. The target is then grabbed by the clawed hand-like organ on top, and immediately disemboweled by means of the razor-sharp protrusion underneath. Grabber-Slashers are very single minded creatures: if instructed to assassinate a particular individual they will stop at nothing until the target is dead, ignoring all other threats to themselves entirely
-Advanced Space Crusade rulebook by Jervis Johnson
Rules
Advanced Space Crusade was the only game where this creature had its own rules. In the table below I've omitted any stats the Grabber-Slasher doesn't have. I've also included the Genestealer profile for comparison.
Name Move. Speed React. Armour Exposed Armour In Cover Weapons Close Combat To Hit Grabber-Slasher 4 9 6 8 Disembowelling Spine 2D+4 Purestrain Genestealer 6 10 10 11 Claws 3D+5
All bio-construct blips were 40pts each. There were separate points for other allies like Genestealer Hybrids. When drawing up a roster you could choose a blip to be one Tyranid Warrior, 2 Grabber-Slashers, 2 Genestealers, etc.
Genestealers have much better stats. However, Grabber-Slashers have a gimmick. They can launch themselves 6 squares into close-combat and their attacks cannot be parried. Both models must fight until one is killed.
I can't say I ever tried these rules out. I had Genestealer models so I just used them.
Model

The model ↗
came on the 25mm base that was standard for most infantry.
In Warhammer 40,000

In the Rogue Trader Tyranid army list the Grabber-Slasher model just appears on the bases alongside other Squigs.
M WS BS S T W I A Ld/Cl 6 - - 3 1 6 1 * 5
The Tyranid player can have a single swarm with one or more bases. Swarms come with a bunch of unique swarm rules. That's why they lack some profile characteristics.
The Tyranid assassin archetype was remade in 2nd edition as the Lictor ↗
, a much more imposing model. Squigs were replaced by Ripper Swarms ↗
.