Nat& Spectrum System - θ∆

Mesh Data Transfer. if, like me, you're starting with an existing model and working backwards to resculpt using a multiresolution modifier, here's a chain you can use to keep your shapekeys on a resculpted and remeshed mesh:

1. use shapekey helper menu to apply the multiresolution modifier at its highest resolution after sculpting, while keeping the shapekeys. this will give you a highpoly sculpted mesh with shapekeys
2. find whatever shapekey results in the least self-intersection and move it to the top of the list, making it the new basis. make the old basis shapekey relative to it, and make sure that setting it to 1 results in your mesh assuming its original shape
3. remesh. i use Quad Remesher because it's nice. now you will have a new mesh, in that shape, with no shapekeys but nice topology
4. use Mesh Data Transfer set to "closest" to transfer shapekeys
   4a. optional: create a UV map on the new mesh and transfer UV set as well
   4b. optional: and vertex groups
5. move old basis back up top
6. set every single other shapekey to be relative to the old basis

now you have a nicely sculpted and retopologied mesh that assumes the shapes of the old mesh properly. good job