Little Badger
OK this idea works in the shifter AU what is the reason vlad called Danny Little Badger was because vlad was actually his biological father and vlad can transform into a badger so say like Maddie had an affair on Jack and that resulted in Danny
But that left the question of how Ellie was made so either he just clone Danny Without using his own DNA as a stabilization or whatever he did I don't really remember because she was kind of unstable in the beginning or he took DNA from Maddie and his own and made another child So that Danny has another sibling without Danny knowing because obviously Danny don't know
There's really nothing else to this idea that's all I could think of
PS Now would be as good a time as any to mention that I have never gotten further than three episodes in Danny Phantom and every detail I know about it is from the fandom I mean I watched it when I was younger but that's Party at best