The Shadows are the agents of the Dark Lord, the Destroyer of Worlds.
During the Passing one shadow agent managed to come over with the refugees, hew was detected and slain by Arach. His body was burned and his ashes were hidden in a secret location.
20 years ago a necromancer called Aradaine was imprisoned beneath Castle Argh, during his attempts to dig an escape tunnel he unfortunately discovered the secret chamber where the Shadows remains were located. Naturally attracted to this type of place and setting he attempted to raise the remains in his service only to be possessed by the spirit of the Shadow. And so the first Shadow returned to the world and began the events that would lead to disaster.
The First Shadow spends 10 years preparing for the First Summoning, where he brings over 13 other Shadows the the Dark Lord, the First Wave. These 13 Shadows move out amongst the orcs of the Zord and begin taking them over, moulding them to become the army of the Dark Lord.
Every 3 years from that summoning the First Shadow is able to summoning another 13 Shades, so in -8 BtF (Before the Fall) he summons the 2nd Wave of 13, in -6 BtF the Third Wave of 13, in -4 BtF the Fourth Wave and in -2 BtF the Fifth Wave.
Each of the Waves is set a specific task to complete in the grand plan that has been devised by the Dark Lord. So the First and Second Waves take control of the Orcs of Zord, preparing them to attack the humans. The Third Wave is used to infiltrate the human Royal Family so as to destabilise them, including possessing the King himself. The Fourth Wave infiltrates the Giants of the Rainbow Mountains to create a powerful ally. The Fifth Wave returns to infiltrate more human organisations in preparation for the War that is coming.
The following waves are planned as follows:
0 AtF 6th Wave - 13 Shades - Elves
+2 AtF 7th Wave - 13 Shades - Dwarves
+4 AtF 8th Wave - 13 Shades - Rangers & Druids
+6 AtF 9th Wave - 11 Shades - East Wilds - Raise the Obsidian Core
+8 AtF 10th Wave - 9 Shades - Dark Elves - Raise the Lesser Obsidian Tower.
+10 AtF 11th Wave - 7 Shades - Protection of Castle Argh
+12 AtF 12th Wave - 5 Shades - Protection of Viriconium - begin construction of the Obsidian Tower.
+14 AtF 13th Wave - 3 Shades - The Summoners, raise the Obsidian Tower.
+16 AtF Summon the Dark Lord.
Each progressive wave of Shades will be individually more powerful then the ones before.