If you want to explore 2D skeletal animation and pixel art, check out the 2D Animation Sample package from Unity. It is a collection of 2D characters that were utilized by internal Unity teams and are now publicly available to users.
The collection features characters of multiple game styles. The animations were created using Photoshop and then animated in Unity, together with professional 2D animators. One of the samples included in the pack is a pixel art version of Unity Chan, which shows frame-by-frame animations of the character and the seamless integration with Aseprite.