The Japanese Imperial Army had two types of Mixed Brigades.
First type was the Mixed Brigade. This was the detachment of an infantry brigade from an IJA Infantry Division with various Divisional support units or sometimes units attached from its Corps or Army. This provided a combined arms force of infantry, artillery, cavalry and other support units.
Second was the Independent Mixed Brigade. These were detachments made of various units detached from other units or independent support units formed together in a brigade.
The first two of these Independent Mixed Brigades, formed by the Kwangtung army in the 1930s was the IJA 1st Independent Mixed Brigade and the IJA 11th Independent Mixed Brigade. These brigades were organized in unique manners and one of them, the 11th was later formed into the IJA 26th Division.
Later a series of IJA Independent Mixed Brigades were formed for the purpose of garrisoning the large territories of China captured in the early phase of the Second Sino-Japanese War.
The original article can be found at List of Japanese Mixed Brigades and the edit history here.