Shrinkbarrels are an object which appear in Wario Land: Shake It!. They only appear in two levels, Bad Manor and Boogie Mansion.
Description[]
A shrinkbarrel has the appearance of a regular brown barrel with yellow left and right directional arrows and two openings, one of which is larger than the other. Wario can enter the large opening to emerge as Mini Wario from the smaller opening. Conversely, Mini Wario can enter the smaller opening to transform back into regular Wario, but entering the large opening as Mini Wario does not have any effect.