"... And Fiona stands with a cry, and that is almost all the warning there is; every flame in the room spits forth a gout of darkness, a tower of black fire, a torrent of incarnate night. Benedict is on his feet, as smooth as an oiled machine, as the tenebrous eruptions split and shower to the floor as perhaps a hundred *things*, each sharp-limbed and inky black, flickering like the fires from which they come. ..."
-- Shavings of True Stone (the game)
Corwin's goblins are creatures of black flame, conjured through real fires from some barren plain. Their arms can be blades; their bodies absorb wounds uncaringly; and, in essence, they want a lot of people dead. There are indications that their unusual nature also gives them unusual weaknesses.

Shavings of True Stone