[kevinp]

Yes, it is a simplified version of the main mesh, it has no material mapping on it & you only need the Vertices & the Faces, the face groups are not needed.

The name of the shadow mesh for the first LOD is [ShVertices_Frame0]
Write it at the end of the first LOD ( underneath [Faces] ) & write your vertices underneath.

Next comes the shadow faces, which are called [ShFaces]
Write your faces underneath it.

For the house in my picture, the text in the .msh file looks like this -

[ShVertices_Frame0]
-10.0 0.0 8.9653 0.0 -0.425134 0.905131
-10.0 -5.0 6.61683 0.0 -0.425134 0.905131
10.0 0.0 8.9653 0.0 -0.425134 0.905131
10.0 -5.0 6.61683 0.0 -0.425134 0.905131
-10.0 5.0 6.61683 0.0 0.425134 0.905131
10.0 5.0 6.61683 0.0 0.425134 0.905131
-10.0 0.0 0.0 -1.0 0.0 0.0
-10.0 -5.0 0.0 -1.0 0.0 0.0
10.0 -5.0 0.0 1.0 0.0 0.0
10.0 0.0 0.0 1.0 0.0 0.0
-10.0 5.0 0.0 -1.0 0.0 0.0
10.0 5.0 0.0 0.0 1.0 0.0

[ShFaces]
0 1 2
3 2 1
4 0 5
2 5 0
6 7 1
1 0 6
8 9 2
2 3 8
7 8 3
3 1 7
10 6 0
0 4 10
11 10 4
4 5 11
9 11 5
5 2 9

Each LOD has its own shadow mesh, so if you have four LODs then you need four shadow meshes & they are named LOD1, LOD2 etc. So, for example, the titles for the next shadow mesh are written -

[LOD1_ShVertices_Frame0]

[LOD1_ShFaces]

It's pretty simple.

Cheers
Kevin