To add a new category to a page you can click the Category button at the bottom of the page and type in the name you'd like your category to be called.
A full list of existing categories can be found at Special:Categories.
“ Maintenance Category This category is used to organize pages on the wiki for maintenance...
“ Exhibition 1 v 1 (Duel), 2 v 2 (Doubles), 3 v 3 (Standard), 4 v 4 (Chaos), Mutator Mashup...
“ For a full list of help pages, see Help:Contents, which includes help pages shared across Wikia.