Blend from Shape brush for sculpting

I often create blendshapes manually in Blender for my VRChat models, and I won’t hide the fact that “Blend from Shape” is something I use extremely often. Maybe it’s just my limited Blender knowledge, but I really wish Blender had a configurable brush that could blend shapes directly from a selected blendshape.

For example, if I’m editing blendshape “1” and I want to restore a bit of the original “Basis” shape, I’d love to simply brush over the mesh and have it smoothly return toward the Basis form. It would also be amazing to have adjustable strength, radius, and the ability to choose which blendshape is used as the source. An “Add/Subtract” mode would be incredibly useful too, so you could either add or remove the selected shape influence dynamically.

The second feature I really miss is a way to compare blendshapes against each other. Right now I use a custom tool generated by AI <forgive me, I can’t code myself>, where after selecting a base blendshape and pressing “Compare,” Blender automatically enters Edit Mode and highlights all vertices affected by that shape key.

Honestly, it’s incredibly useful for finding mistakes or accidental vertex movement.

Edit about brush: I hear ZBrush have option like this called Morph from Target