The background looks terrible and the set looks cheap. Big dog is always changing in very strange ways, consisting of size, shape, and thickness of the character. The plot was lazily thrown together, only making this worse is the fact that there is nothing to really see on the reason for his revenge. Flashbacks can be good, but in some instances it shouldn't be relied on if the entire animation is about that flashback. As well as that, this wins second place for the cringiest movement style (Losing to planet outcast 3056) mainly consisting of slow and choppy animations. As a bonus, classic cartoons are slightly energetic and have some cute ways of breaking physics (ex. arms stretching to empathize reaching and stuff) however, this animation seems to be more bland than a live action movie made by Disney channel. Just no, rework it.
The thing you did right: decent intro. not going to call it a masterpiece though, just better than the entire animation.