Moving armature deforms mesh

Greetings guys and gals!

I’m pretty noob at Blender and trying to learn as much as i can from different tutorials. My current project is to import some models from the videogame League of Legends and rig them so I can pose them and later export them so I can 3D print them (if you are wondering, no, I’m not going to sell anything. It’s just a hobby I enjoy).

So far everything is going well until I use Armature Deform with Automatic Weights. The mesh of the model deforms way too much when I move bones with the Pose Mode, hopefully this gif explains it a lot better:

I read that this usually happens with Automatic Weights and that I can use Weight Paint to adjust this. The problem is that a few vertex are still being dragged even after I used the substract paint.

Also, there’s this tip of the chain at her legs that for some reason decides to move as well (I suppose it’s probably because of the same reason).

Do you know what can I do to fix this? Please consider I’m a total newbie on Blender, so a detailed explanation is much appreciated :slight_smile: (I can also upload the file if that helps!). Thanks!