In the picture, you see how that face doesn’t get pulled with the rest after I rotated the bones? Can anyone please tell me why? I am 100% sure all the faces on that thumb were assigned to a bone, but this bit won’t move? Please, any ideas would be awesome. Thanks in advance,
Enable the armature modifier to work while the mesh is in edit mode… (triangle icon at the top of the modifier)
Enter edit mode for the mesh while posing it like you have pictured, select a vert that isn’t working correctly and look in the transforms panel. There will be a listing of what vertex groups the offending vertex is assigned to. It is possible to weight a vert 100% to 2 or more different bones, I’m thinking it’s also weighted to another bone, like maybe the upperleg bone shown in your pic.
Did you weight paint this? If so, you could also go into weight paint mode, enable auto-normalize in the tool shelf, and weight the verts to the correct bone, the auto normalize will subtract weight from other groups as you add weight to one group.
Edit: ps…Welcome to ba.org!!