Overall, I think is very amazing! I like the idea of the roles reversed and the character being bad instead of good. Feels very original and fresh. I do like the style being attributed to the old cartoons of the 2000s. I can see the Invader Zim influence. The zaniness and creativity is definitely there. Even the VA and sounds are used perfect timing. I think 8/10.
I do have a bit of constructive criticism here now it could just be my personal opinion but this is from I learn in terms of design. I feel like some of the background blended in too much with the characters. Ex: the bathroom scene. I definitely understand why you have the colors there but some colors felt like they were too bright or too similar. Try to focus on who you want to be the main focus (but you definitely do that but some colors look like they pop out more). I'm not sure if there's a way, but try to check value work on the scenes. Backgrounds are great to make and all but don't make them the main point unless you have to.
Ex: The scene where Spike is waving his hands for the plumber. I can see the hair of Spike catching my attention but then so does the red in the stall and the green of the mirrors. I'm not sure who I'm supposed to be paying attention to. Unless it's in this case both, I can understand but I feel like it's been established they're in the bathroom already. I'm sure there's an example of where you can do the background and the character as the main points.
The animations work fantastic for the zaniness and craziness of this world but some animation felt a bit too fast. Also some camera work felt like the balance of some scenes were off. Ex: plunger caught in the hand. Kind of felt off and weird.
Apologies for the long comment here this is just my personal opinion. I'm a student who's got knowledge in animation and design. Seeing stuff like this reminds me of what I also want to do. And I want this to be successful! This really has high potential. I hope my criticism isn't too harsh, it's just what I know learning from school.
If you ever need help or so, let me know. I would love to continue to help from my knowledge in any way from character design to storyboards (also have knowledge in screenplay). Overall, good luck to this and other future projects!