From EFWiki

Mutants and freaks, forever outcast from Hive City and doomed to wander the Underhive scourging for basic rations to survive. In areas of the underhive, where there is no Enforcer presence, Scavvies are known to trade with local guilders and are marginally more accepted in society. However the nature of scavvies means that there is always a bounty on their heads and many of the Underhive make a living hunting the members of these mutant clans.

Scavvy gangs work in a similar way to the houses of Necromunda whereby many scavvies muster under the banner of a single leader, a particularly tough and influential individual. The Scavvie Boss will always be accompanied by a retinue of either Plague Zombies, Scavvie Dogs or Ghouls. In addition, Scavvie Bosses can make the highly dangerous Tox Bombs.

From various contact with House gangs in the underhive, it has been discovered that there is also a new breed of Scavvie: Scalies. Over generations, Scalies have become so badly afflicted by the toxic conditions of the underhive that they barely resemble humans at all. They have grown tougher, scaly skin and their strength has become comparable to that of a Imperium's bio-engineered Ogryn.

By order of enforcer authorities the Scavvie menace is to be terminated whenever and wherever it is found. Good hunting!!!

[edit] Scavvie rules

See the Scavvies entry in the Fanatic Online Articles section.