I'm not entirely sure what 'rated m fanfiction' means in this context. It could be that Veruca and her dog are somehow related to a fan - created story that has a certain maturity rating, perhaps indicating it contains some more complex or potentially adult - themed elements. But without more information, it's hard to say exactly.
It's possible that 'Veruca' is a character, and she has a dog. The 'rated m' might suggest that the fanfiction related to them has some content that is not suitable for all audiences. Maybe it contains violence, strong language, or more complex and adult - like themes. But again, without reading the actual fanfiction, it's just speculation.
The kid stroller cartoon often has colorful and cute designs. It might show kids having fun while using the stroller, and maybe some funny adventures along the way.
The cat in the cartoon could have a lot of significance. It could be a central character teaching valuable lessons, or it could just be there for entertainment, making people laugh. It all depends on the creator's intention and the story they want to tell.