Orc and Goblin shamans blast the enemy with waves of Waaagh energy. Waaagh spells tend to be crude but effective, low on subtle manipulation but big on raw power.
On the tabletop Orc and Goblin shamans act as a focus for the power of the Waaagh. Waaagh energy pours into their brains from the excited Orcs and Goblins around them. The shamans must constantly try to build up the power to a critical point and then release it before it is lost or (ulp!) their head explodes.
The following is an excerpt from pages 28 & 29 of the Warhammer Arcane Magic supplement in the Waaagh! Magic section.
Shamans who are more than 12" away from any eligible Orc or Goblin units can't cast spells at all, though they may still dispel enemy magic as usual. In this case the shaman need not take a Waaagh test.
Night Goblin Shamans
Night Goblin shamans start the game with one piece of magic mushroom per magic level. Each piece may be used once during a game.
The shaman may eat a piece of mushroom at the start of any magic phase, before the Winds of Magic are determined, entitling him to D6 extra magic cards to be used in that magic phase only.
If a Night Goblin shaman has consumed a piece of mushroom he may cast spells even if there are no Orc/Goblin units within 12" to supply Waaagh energy. In this case he is dealt no cards from the Winds of Magic, but is limited to his D6 extra cards.
If the Night Goblin shaman has eaten a piece of mushroom, and fails his Waaagh! test, deduct -1 from his roll on the 'Eadbangerz chart.
Forest Goblin Shamans
A Forest Goblin adds +1 to his score when he rolls on the 'Eadbangerz chart. If he rolls a 6+ he is completely unaffected.
Every time a Forest Goblin shaman fails a Waaagh test he staggers D6" in a random direction (use the scatter dice to determine which).
This happens even if he rolls 6 on the 'Eadbangerz chart.
Move the shaman before applying the 'Eadbanger results. If he moves into an enemy he becomes engaged in hand-to-hand combat and must fight in the following hand-to-hand combat round (and counts as charging). If he is already in hand-to-hand combat, he will not move away, but counts as charging in the next round.
Savage Orc Shamans
If a Savage Orc shaman joins a Mob of Savage Ores he gets an extra magic card when they are dealt at the start of the magic phase. The bonus card may only be used by that shaman. In addition, the shaman's protective tattoos now give him a saving throw of 5 or 6 rather than a 6. The Savage Orcs' tattoos also give them an enhanced saving throw of 5 or 6.