Model mesh warps and deforms upon adding rig

No idea what’s going on here but need help rather desperately. Spent ages setting up this rig, when I attach it to the model it warps like the one on the right.
Model is from turbosquid and came pre-rigged but the rig wasn’t happy inside blender so I removed it.

Things I’ve tried:

  • merging all his parts before parenting the rig as well as parenting him as separate parts.
  • applying scale on both him and the rig
  • deleting all the vertex groups

Hard to tell without blend but check all your transforms are neutral or applied before parenting on both armature and model. Check to be sure you don’t have rogue modifiers on.

Just to put stilltrying’s words into something a little more casual: your armature’s rest pose needs to be the same pose that your model is in. You can’t pose it in pose mode to match the model unless you apply the pose. And applying the pose might screw up some constraints, if you’re using any. (Looks like a rigify metarig? No constraints on that.)

Beyond that, it also looks like you’re trying to weight a mesh with multiple, disconnected meshes. Autoweights don’t work well on those kinds of meshes. This one will require some manual painting.

yeah I think I posed it in pose mode vs edit mode. One other question, you say it won’t work on separate meshes, can I join them and have it work? or will I need to actually stitch verts together so it’s a continuous mesh?
edit: I started over with the metarig, and this time when I bound the character to it, I got a heat weighting error. That was the collapsed mesh, I tried again with separate meshes and it pretty much worked. Only thing is, some parts of the mesh float off when posing because they’re getting caught in the… vertex groups or something?

You’ll need to actually stitch verts together. The reason they float away is because they’re an autoweight of unstitched meshes.

If you’re using merge by distance, you should make sure that you’re only merging verts that should be merged. It’s possible to for some meshes to become non-manifold from a naive merge-by-distance, which would explain the “bone heat” failure.