Hi, I'm still finishing up that eeveelution accessories mod, and I'm having trouble with what I hope is the last roadblock I encounter.

I'm making Sylveon's bowtie, and because I'm sure the mesh would break beyond repair if I wrapped it around the arms, I decided to have it drape down the sims shoulders, the issue is I cannot for the life of me assign bones in a way that doesn't utterly break the mesh. Images below on what I'm doing vs what the mesh looks like in TSRW. I'm still pretty new to this stuff, so looking to hopefully get answers from somebody who's more familiar with all this, anything helps, thank you!

Personally, I would weight paint it like a long hair would be - just with Neck as the main bone instead of HeadNew.
Select the entire mesh and assign Neck. Then switch to Weight Paint mode, and CTRL + Num Pad 1 to look at the back in orthographic view. Use the Gradient brush to apply Spine2 up to the base of the neck, then Spine1 on everything to about mid-shoulder-blade. I like to Normalize All from the Weights menu after each step for finer control.

If desired, clavicles can be added last with the Gradient set to Radial.
I can attach a screenshot if that would be easier to visualise.

However, the way you have it now doesn't look like it would cause the issue in the TSRW screenshot - is it possible some stray verts in those areas accidentally got assigned to Neck? I'm not sure if the TSRW preview actually shows bone influence - it's possible it's actually a morph causing that distortion. Either way, you could confirm by selecting the entire mesh, assigning a single bone, and then see if that area is still distorted.

You have opened a can of PITA! But, doable. Problem is I haven't used what looks like 2.79 in years, and can't show you with that version. I'm using 2.93. What you have is influence from arm bones. Most likely bicep. Your project is easier than a cape, so that's good.

What I do is import the garment as geom, and matching body geom. In Blender 2.8x and up, you can then import the rig to match the gender/age. Select all parts, and last the rig, then Object> Parent> Armature Deform. The body and garment are now attached to the rig. Select the rig and go to Pose mode. Select a shoulder, and rotate it. Watch your mesh distort. The goal is to get all of the bones to move the garment as YOU want... or as close as possible!






You might first simply delete all arm bones from the garment, since you appear to want this to drape the body, and NOT follow the arms, as with my cape.

When painting this type of garment, you can mask off just the area you want to paint. Use the gradient brush, and experiment with linear and radial, and weight, size of brush, and strength.

Normalize after painting, and remember your best friend, the undo button!!!




But again, you probably want to just delete arm bones that influence your garment.

NOTE: The gradient brushes will paint front and backfaces at the same time, so no guessing as when using the regular brush.