One popular 'isekai ojisan light novel' could be 'Isekai Ojisan: Isekai ni Tensei Shita Kedo Cheat Nanka Shinai yo'. It tells an interesting story about an uncle who gets isekai -ed but doesn't have the typical cheat skills.
I'm not entirely sure as I haven't read it in detail. But generally, it might be about some sort of fantasy story involving a bishoujo (a cute girl character in Japanese media) and an ojisan (uncle or older man) in a novel - like setting.
I'm not sure who the main characters are exactly as I don't know this work well. But from the title, it seems that a bishoujo and an ojisan would be important characters.
The relationship would be filled with new emotions. There would be moments of stress, like when the baby is sick and they don't know what to do. But there would also be moments of great joy, like when the baby takes its first steps. Through all these experiences, they would understand each other better and their relationship would evolve into a more complex and loving one.
I'm not sure which specific 'Mabel ghost story' you're referring to. There could be many fictional or local tales about a ghost named Mabel. It might be a story passed down in a particular family, community, or written by an unknown author.
Bill Cipher would be an interesting character to involve. If he shows up, he could be even more manipulative towards Reverse Dipper and Mabel. His chaotic nature could create a lot of conflict and drama. Reverse Dipper might be more vulnerable to Bill's tricks or perhaps more resistant in some unexpected ways. And Mabel would have to use her wits and kindness to try to counter Bill's evil plans.