Introduce a cat into your comic strip and its popularity increases.
But the cat also can take over the strip.
Back when I was writing a lot of articles about cartoons and the Internet, I heard this from a number of artists. People love cats in cartoons. Perhaps 97% of comic strip readers are elderly ladies? I dunno. But it's just how it works. It's why Garfield has remained ridiculously popular. (Although I started reading the strip again recently, and it seems strangely fresh and amusing. How did that happen?)
In Arlo & Janis, there's Ludwig, a late addition to the strip that often gets entire days to himself. In 9 Chickweed Lane--a strip that has largely relocated its characters to Manhattan--you'll find Solange, who turned her behavior into a book.