I remembered that User:Molothrus Aeneus made her own list of ideas, so I decided to make my own ideas for the sequel.
1. Snowball joins the gang: Ever since the end of the first movie, Snowball now lives in the apartment. SO maybe Snowball can join the group.
3. Max and Gidget: Ever since the end of the first movie, they seemingly get along. (I do not know if they will be a couple because apparently Max is fixed, as he gave advice to Buddy and Mel about it to stay the comfortable way.) I wonder if it talks about their relationship and maybe another dog tries to get Max's attention. Like a love triangle.
5. Katie to appear more: She should appear more in the sequel, I would agree with User:Molothrus Aeneus (who, by the way strike-throughed it in her blog) on her needing to appear more. I mean Lucy Wilde and Scarlet Overkill gets a lot of screentime in their respective movies, so why not Katie too?
6. Katie's Job: It's unknown what her job is. Maybe the sequel will say what it is. Plus, it should talk about her being a musician as there was a violin in her apartment and some trophies. (Maybe there should be a spin-off movie about this).
7. Katie gets a boyfriend: Perhaps Katie has a boyfriend who could also be the movie's antagonist. This is like an allusion with max and Gidget being a couple. Perhaps he hates pets and attempts to make Max and Duke look bad in front of Katie so she would get rid of them. And maybe the apartment pets try to get rid of him and maybe the flushed pets (Derick, Tattoo, Ozone, Nitro and Dragon) can help.
8. Brooklyn Eastern District Terminal Showdown: It would be cool to show the Brooklyn Eastern District Terminal railway area. It would be a cool place to have a climax. There are a multitude of trains there that can be part of an action-packed scene.
9. Damsel in Distress: Perhaps Katie scolds Max often in the movie, and when she's in danger, Max saves her life and she forgives him, as well as him impressing Gidget with his heroic acts.