How to add inbetweens to blend shapes
This tutorial is a little advanced, but its something i learned recently and wanted to share!
So to do this you’ll need the 2 key blendshapes as well as the inbetweens you wish to add to them, for this, i have 2 key blendshapes (far right and left) and 2 inbetweens

Step 1: Select your last then first mesh, make sure they are aligned on top each other!

Step 2: In the rigging menu, go to the Deform tab, then choose blend shape

Step 3: Name your blend shape and click ok, i just called mine “shirt”

Now when you click on your first mesh, you should see an input called shirt, plus a slider under the envelop, when you move this slider from 0 to 1, it should change into your last mesh

Step 4: Adding the inbetweens, I dont like how my shirt deforms when the slider at 0.3 so i want to add an inbetween to the shirt, specifically the mesh to my left

Click the your inbetween then your first mesh, again, make sure they are aligned!

Again in the rigging menu, click the deform tab then scoll down to find Blendshape, then click the box next to Add

This box should appear, in here, check on add in-between target, and change the slider of when you want your inbetween weight, i have mine at 0.3 since that is the point when i thought my shirt did not deform properly
after this, click apply and close

Step 5: repeat step 4 for any remaining blend shapes

Your final product should react like so!



















