When Kurgaz forged the Anvils of Doom many centuries ago the most potent rune they had beaten onto them was the Rune of Doom, after which they were named. However, this rune is so difficult and dangerous to use that its secret has almost been lost. Some have not ever dared to use it or have never seen a threat they deemed sufficient to warrant its power. Others have tried and failed to contain and focus its might and their anvils have been torn apart by the uncontrolled energies. Today, the only remaining Runelord who has the skill and courage to attempt it is Thorek Ironbrow.
When this rune is struck, the air grow chill and the skies turn dark. Ghostly forms of ancient warriors appear amidst the Dwarfs on the battlefield, bolstering their ranks and their courage. These are not ghosts as such, but a manifestation of the Dwarfs' own grim and doom-laden nature. Their anger at the loss of their mighty civilisation and the desecration of their Holds fill them with a righteous fury that is terrible to behold, and their normally grim faces are set with an expression of black vengeance.
All the Dwarfs in the army cause fear.
Once cast the effects of the Rune of Doom last until it is dispelled, until Thorek chooses to end it (which he can do at any time), uses another rune, or is slain.
However, if you miscast when rolling to cast the Rune of Doom then disaster has struck. The power of the rune tears the Anvil asunder. Thorek, Kraggi and any surviving Anvil Guard each take a single Strength 7 hit from the blast. The Anvil is destroyed and the survivors form a skirmishing unit.
Note that as you've been reminded of the doom of your race and that your Golden Age has long passed you should feel free to grumble about it (and don't forget to mention that it's the Elves' fault). This has no game effect, but is entirely in character and may make you feel better.