How I Met Your Mother Ending: 10 Past Faults It Must Avoid
5. Less Babies

I have never been sold on the idea of introducing a small child into tv shows. It's rarely handled well, and just slows down the pace. This is usually done out of desperation, too, and reeks of trying to interject some false shot of adrenaline into a waning show. It never sits well with me, and it didn't when HIMYM introduced Marvin, either. While he's been handled somewhat well in terms of not crippling the show, I still believe the finale needs less babies, more of the adults we've come to love.
This is still a story about these five people, and yes, two of them have a baby together, but that means literally nothing in the context of its series finale. It needs to be about them. I'm not saying completely remove Marvin and leave him out entirely, but a minimum of scenes is absolutely necessary. There's no way, in an episode this big, that you can exclude the child of two of the main characters, but some restraint would be very much appreciated.