Many large and powerful creatures are unfortunately rather stupid. Even some otherwise quite intelligent creatures act stupidly now and again because they are easily confused or distracted, or perhaps because they are under the effect of a spell. The Stupidity rules represent the sort of slow-wittedness or dumb behaviour that some especially thick beasts are prone to. Creatures that are Stupid are indicated as such in the Warhammer Armies books and include such models as Trolls and Cold Ones.
Stupid creatures that are not engaged in combat must make a test at the start of their turn to see whether they overcome their Stupidity. Make a test for each unit of Stupid troops. If they pass the test, all is well and good - the creatures behave reasonably intelligently and can move as normal. Nothing untoward has occurred beyond a bit of drooling and the odd spontaneous cackle.
If the test is failed, all is not well and the unit momentarily forgets what it is doing. The unit is moved directly forwards at half speed during the compulsory moves part of the movement phase (for example, Trolls with Movement 6 would move 3" forward). Skirmishing units will move at half speed in a direction determined by rolling the scatter dice.
This counts as compulsory movement and so occurs before other movement, but after charges have been declared (see the Movement section) Any enemy troops encountered are automatically charged. This is then treated as a normal charge, except that the charger will move only half its normal Move rate (3" in the example above), regardless of the outcome of the charge.
If there are friends in the way, the units blunder into each other and their ranks become confused, in which case both units are pinned in place for the rest of the movement phase and neither may move further.
Units that failed their Stupidity test cannot voluntarily declare charges, shoot and cannot cast spells for that turn.
These rules apply until the start of the creatures' following turn, when they must test once more to see whether they are affected by Stupidity. The effect of Stupidity also stops immediately if the creatures are engaged in close combat, as their fighting instincts overcome their Stupidity.
Other Psychology
Creatures affected by Stupidity are quite unaware of anything happening around them. Until they are no longer Stupid, these units are Immune to Psychology.
Stupidity and Riders
It sometimes happens that a cavalry rider or a monster rider will be riding a Stupid creature, for example, a Dark Elf riding a Cold One. If a rider's mount is Stupid, it will have to test for Stupidity at the start of his turn, but the rider's Leadership characteristic is used rather than that of the mount. If the test is failed, the rider is obliged to hang on and is unable to shoot and cast spells while the creature is Stupid.