From Warhammer-Empire Wiki
Gut Magic or Gastromancy is unique to the Ogre army, and consistes solely of rather gory spells cast on just a 3+. An Ogre player will often cast many of these spells using a single power dice each. Gut Magic is only usable by a Butcher or a Slaughtermaster.
Gut Magic's primary purpose is to increase the fighting potential of Ogre units. Ogre magic works slightly differently than conventional magic in several key aspects. First, a Butcher knows every spell in the lore, and can cast each one once per magic phase (power dice allowing.) Each spell is cast on a 3+ to start, with successive casting increasing the difficulty by 3. Secondly a Butcher can maintain more than one "Buff" spell at a time, on different units. These spells are treated like Remains in Play spells in subsequent turns, but can be dispelled on a 7+ no matter what the original casting cost was.
A quick review of the spells and their uses:
Bloodgruel - This spell heals a Butcher by one wound, provided he rolls a 2-6 on a d6. On the result of a one he loses a wound, making this spell a little bit risky when down to one wound.
Bonecruncher - Deals 2d6 Strength 2 hits with no armour save to a unit within 18" line of sight. The Butcher takes a Strength 4 hit on completion of this spell. Bonecruncher is exellent against low toughness, high armour units, like Knightly Orders, or Bretonnian Knights.
Braingobbler - This spell is very dangerous to low to average leadership armies like Orcs and Goblins and Empire. Braingobbler forces a unit to take an immediate panic test. This spell is even more dangerous when coupled with a couple of items that give Leadership penalties.
Bullgorger - An under rated spell by some Ogre players, Bullgorger gives a unit +1 Strength, which is an excellent bonus when coupled with a unit that has lots of attacks like Bulls with extra hand weapons, or Maneaters with Braces of Handguns. To successfully cast this spell a Butcher must pass a Strength test, or the spell fails.
Toothcracker - Possibly the most dangerous spell available to a Butcher, Toothcracker gives a unit +1 Toughness AND makes them Stubborn, which helps offset the Ogre's lack of static combat resolution. This spell causes a Strength 6 hit against the caster when it is successfully cast.
Trollguts - Upon successful completion of this spell, the Butcher takes an automatic wound but he grants an Ogre unit Regeneration and Magic Resistance 2. This is a very useful spell for units that must weather sustained gunfire.
Dealing With Gut Magic
Because of Gut Magic's unique mechanics, it requires a unique strategy to deal with it. In the first turns before combat is joined, it is important to use Dispel Dice to dispel to stop Braingobbler and Bonecruncher from damaging your lines. Let the buffs go through and most likely put a wound on the caster, then use Power Dice to dispel them in YOUR next magic phase. Once a Butcher is wounded, be sure to dispel Bloodgruel if possible, it will make your opponent reconsider casting his buffs.
Once combat has started, use your Dispel Dice to stop buffs from going through. Braingobbler and Bonecruncher will be less of an issue now because most units will be either in combat or out of line of sight. When faced with Empire guns, a smart Butcher will be in combat as soon as possible, so after the first two turns, you can expect to see an end of attempts to cast non-buff spells.