[Would it be copyright infringement to use copyrighted characters to demonstrate my animation skills?]

Thanks for your input. The reason I haven't created my own characters is because 3D modelling is a skill that I've attempted for years and still haven't grasped it. Anyway, I had also messaged Fiverr support and the response I got is that since I would be making the animation, it would be my own work.

[Would it be copyright infringement to use copyrighted characters to demonstrate my animation skills?]

I wanted to set up an animation gig and I want to make a short video demonstrating my skills so that buyers can be confident when the purchase from me. I was wondering if I were to animate copyrighted characters for the demo video (Sonic, Ninja Turtles, Spider-Man, etc) would it be considered copyright infringement and would Fiverr take down my account? Thanks.