Here are a list of creatures and races that have been only mention either once in the source material or has very little information on them
Races
Urkin
Mentioned once in Kings of War - 1st Edition Rulebook page 119
"Wherever there are Orcs, there are their kinsfolk, the Goblins and Urkin. Lesser creatures than the Orcs, what the Goblins lack in size they make up for in viciousness"
Half-orcs
Mentioned twice in Kings of War - 1st Edition Rulebook on page 118 and 119
"Roving hordes of Orcs, Goblins, Hobgoblins, Half-Orcs and worse, accompanied by all manner of monsters and war engines, are a constant threat to the realms of finer folk" "Lesser creatures than the Orcs, what the Goblins lack in size they make up for in viciousness. Many other sub-species of Orcoid curse the world - Greater Goblins, Hobgoblins and the vile Half-Orcs."
Greater Goblins
Mentioned once in Kings of War - 1st Edition Rulebook page 119
"Lesser creatures than the Orcs, what the Goblins lack in size they make up for in viciousness. Many other sub-species of Orcoid curse the world - Greater Goblins, Hobgoblins and the vile Half-Orcs."
Creatures
Vargen
Mentioned in Mantic Journal 4. Owned by Orcs.