Hi.
The thumb glitches because it was accidentally painted with b__R_Pinky2__. To identify which vertex group is causing the problem:
1-2). in Edit mode select vertices ( one at a time ) in this area until you find a group that does not belong there;
3-5). Click on + button and type in Pinky2. Select the group and then press Select button;
6-7). Disable Limit selection to visible and, holding Ctrl, lasso-deselect vertices on the right hand;
8). Choose Remove;
9). Switch to Weight paint mode and click on Normalize all.
Every part of the nude body that MD mesh covers should be deleted. In the place that is left you should put the MD mesh's UVs. Putting them in the
extra space is a bad idea because many creators do and that can lead to overlapping of textures.
1). In 3D view select everything with A. In UV editor activate sync. Press B to activate box selection and select all MD mesh's UV islands;
2). in 3D view press P and choose Selection to separate the dress from the body;
3). Switch viewport shading to solid to see the wireframe better;
4-5). Select everything that is covered by the MD mesh leaving one loop of vertices at the bottom to prevent holes from appearing in the process of walking;
6). press Delete and choose Faces;
7-8). You can select edges as I did and in the pic and dissolve them;
9-10). Once done, select everything and set the background image. Shift-select the dress, switch to Edit mode, select everything, set the same exact background image. View- Draw other objects to see the body's UVs.
11). S to scale, G to move, R to rotate. S or G followed by Y/X will constrain modifications to the vertical/horizontal axis. R followed by a number will rotate the selection by this number.
Place them like this so that it would not overlap with the body's UVs.
After that transfer the uv_1 map as shown
here from 2:37 to around 4 minutes. Choose Nearest face interpolated instead of the default one.
Once done, select the dress, Shift-select the body, hit Ctrl J to combine.
I suggest to not use Decimate modifier to reduce the polycount. You can either
switch to quads and raise
Particle distance of some patterns or, if using MD 8,
Remesh everything. Both options are bad but still will give you much better results than Decimate. Ideally, you'd want to retopologize the mesh. It can be done in
Instant meshes,
Blender or, the best, Zbrush. Anyway, the second dress is flying because you need to use Clean tool after transferring weights in newer versions of Blender.
Shown here from 2:09 to 2:40.This dress is unnecessary highpoly, you shouldn't go past 10-15k.
Also, for the future, when sharing packages with us here, please either don't change this name or tell us what CAS item was cloned to start the package.