This feature likely doesn't exist because it would be a lot of work for the dev team for absolutely no gain. Creating a new tag takes a matter of seconds, and handling the occasional tag creation request from new users doesn't take much longer.
You're not the first person to want this functionality either for the mobile site or the official apps. Mind you, you can get around it by going to the full site on your phone as a workaround, or by using a different tag and leaving a comment asking for someone to add the proper tag.
There is a feature request to add this functionality to the mobile site, ...
A tag cannot exist without a question. If you have a question about said game, just ask it and tag it with pc or something, but do mention in your post about what game you are talking, so someone with enough rep can add the tag to your question.
Welcome to Arqade!
The reason we don't allow just anyone to create tags is because we want to make sure that the tags are useful and follow our general guidelines in terms of tagging. It's basically a sign of trust - we know you've been around long enough to have a pretty good idea of how we do things, so we let you participate more and more.
That said, ...
Ask the question anyway using an as close to approximate tag (in this casepokemon-series would do nicely) and
mention the title in the question (ie. in Pokemon Tretta _______) and/or
at the end make a request for a tag (ie. request pokemon-tretta as i do not have enough rep to create it)
someone with the privilege will very likely comes across the question ...
To expand on what Wipqozn states: Autogenerating tags sounds like a good idea in theory, but the practicalities of implementing this would mean a lot of work for very little (if any) gain.
Where would this automated tag generation system pull it's list of games? Who maintains the list of games? Anything built by SE that pulls stuff from say Wikipedia, or ...
Tags cannot exist without questions asked. If no one has asked a question about Hybrid Animals, then the tag simply won't exist in our board. If you have a question for that game, ask it. If you don't have enough rep to create new tags, do your best to tag it appropriately, and another user with higher rep will assist.
Tags need questions in order to exist. If you have a question about these topics, feel free to ask a question, and give it a tag like pc, and a user with permissions to create tags will come by and create a more appropriate tag for you.
As for scrabble, such questions might be better suited at another site on the network, Board and Card Games, but it ...
In addition to what @Ash mentioned, (if you have at least 20 reputation) you can also drop by chat, and ask someone there to create a tag for you. Usually there are quite a few high reputation users active in that chat room who would be more than willing to help you out.
I think after making a question you can flag it for moderator attention with the other reason and then just ask them to make the tag.
Apparently >300 rep users can make tags: https://gaming.stackexchange.com/help/privileges/create-tags
So as Robotnik mentioned, just leave a comment asking someone to create a tag.