Ash's mom's companion Pokémon is a Mr. Mime, but we have reason to believe that the two of them might be a little more than just friends
For the most part, Pokémon spend their downtime inside Pokéballs after being caught by a trainer. However, there are a lucky few who get the chance to remain in the outside world. Pikachu is the first and most famous example of that. Pikachu follows Ash around in the anime series and even walks behind the trainer in Pokémon Yellow.
Companion Pokémon is a trend that continues to this day. Niantic has even added the feature to Pokémon GO, labeling them Buddy Pokémon. Treat them right and they will appear on the map alongside your avatar - and even bring you gifts. As for the aforementioned TV show, Ash's mom Delia has a buddy Pokémon of her own. A Mr. Mime.
Delia shows up with her Mr. Mime in Sun & Moon while visiting Ash in Alola. This is strange for a few reasons. As far as we know, Delia isn't a Pokémon trainer. She might simply have Mr. Mime as a pet, or to help her around the house. So why has he come on vacation with her?
Perhaps the Pokémon and Delia are a little more than just friends... if you know what we mean.
For what is effectively a TV show for children to come out and say a human is having a sexual relationship with a Pokémon is never going to happen, of course. There have been subtle signs, though. The screenshot above, for example. While Delia is talking to her son, Mr. Mime is sat on the other side of her with his hand on her thigh/hand. That's a little forward for a Pokémon, even a buddy one, but Delia doesn't seem to mind one bit.
There is every possibility that Mr. Mime is just a highly intelligent pet. Cats and dogs put their paws on their owners' laps after all, and some even vacation with them. Just because Mr. Mime is bipedal and looks and acts like a human his relationship with his owner just seems a little...off.
There's also the theory that the Pokémon is Ash's biological father, but we're going to need a whole new article before we open that can of worms.