A Triangular Box consists of a Diagonal Line of 3 and a dancer in a corner position of the 3 x 3 Matrix defined by the Diagonal Line. Work with these dancers in a Distorted Box. Triangular Boxes are most commonly used from Interlocked Blocks [C1].
A Triangular Box is a 4dancer formation in the following shape: 
From Interlocked Blocks, there are two Triangular Boxes: to find them, divide the formation in half along the phantom long diagonal. Alternatively, look for a Diagonal of 3, then find the lonesome dancer.  
Other examples of Triangular Boxes: 
Triangular Box Counter Rotate 1/4 :
