To cover all three of your questions:
No mobile tag & adding tags
The reason for no mobile tag on WB.SE is because this stack cannot do anything about the mobile app and therefore have limited questions about mobile (i.e. nobody has actually asked one and thereby created the tag). Though you can ask here, typically questions about mobile should be taken to the Main Meta for Stack Exchange unless they are a specific issue with the sub-site (for example: MathJax rendering on Math.SE would be asked on Math.SE's meta over the Main one).
In fact, there is a question on Meta about this exact issue so you may want to add a new answer there or create a bounty for more attention.
Also note: the mobile app is not well supported (Google even dropped the SO one due to lack of development) and the current answer by SE seems to be "we're moving to responsive websites so we won't need an app".
I would open a new question about that stating your case as currently I don't see a situation where we couldn't just use super-powers, magic or supernatural, or a science based tag (nano, bio, etc) depending on why the person has pyrokinesis.
I'll note, in that vein, that the pyro tag you made on your question should just be magic. It will also likely be deleted (automatically) if it is not used again within 6 months and - after a quick search - this is only the third or fourth questions dealing with pyrokinetics since the site started and the others all used magic, super-powers, or technology.