Genestealer
From Exterminatus Manual
++Tyranids++
Tyranid Genestealer (Stealer)
Overview
Genestealers are the infiltrators and shock troops of the hive fleet. Moving years or even generations ahead of the hive fleet, the infiltrate and corrupt the civilisations they find, weakening them from within. Genestealers are the smallest tyranid creatures on the battlefields of Exterminatus, but they lighting speed, amazing agility and rending talons more than compensate for their small size.
Weapons
Genestealers are armed only with their Talons, leap ability and developed cunning. Primary attack lashes out with the talons, make many rapid strikes. Secondary attack uses their connection to the hive mind to highlight a target for other tyranids to attack (this highlight will even be visibble through walls). Genestealers can also leap by pressing the SPRINT an JUMP keys at the same time. Leaping makes previously inacessible ambush spots reachable. Leaping drains all the stealer's energy, preventing them from making sucessive jumps, but they can recover quickly.
Tactics
Stealers are one of the only class in Exterminatus that doesn't have a gun, but they can earn points at range by scouting out targets for other tyranids to attack. Use your leap to get behind the enemy lines and ambush them, it takes very few talon strikes to take down a marine. Talons can even rip through heavy armour, making them one of the better classes for taking down terminators and dreadnaughts... if you can get close enough.