Bigwigs had a thin stem topped by a purple cap. Each one grew to about 4 inches (10 centimeters) tall.
Consuming a bigwig caused the consumer to double in size and increase in weight eight-fold (as if affected by an enlarge spell) for one hour. Consuming more than one of these mushrooms did not cause further increases in size, but did extend the duration of the affects by another hour each. A few minutes before the effects wore off, the consumer would feel a slight tingling before reducing back to normal size.
Bigwig mushrooms lost their size-changing affects if taken from the Whorlstone Tunnels for more than an hour.