Wikia has a "feature" for unregistered users that forces the TOC (Table of contents) of articles to be unconditionally collapsed. Even if the unregistered user clicks on the link to expand the TOC, when the user loads another page it will have the TOC collapsed again. MediaWiki's collapsible TOC stores a cookie in the browser to remember whether the user decided to collapse or expand the TOC, but wikia forces the TOC to be collapsed on every page load as if the user clicks on the collapse link, defeating that purpose.
Since the TOC is expanded by default for registered users, one may want to have it expanded also for unregistered users so they have a consistent user experience™. Also, an expanded TOC helps tables and images to be pushed down by it and solving the problem of the small width of the content for Oasis when floating infoboxes are present on the page.
Unfortunately, there's no way to fix it since wikia's code run earlier than any wiki-wide or personal custom code, and there's no simple way to check if the user wants the TOC collapsed or not.
How to make the TOC uncollapsed for unregistered users Edit
Since there's no way to disable this wikia feature, there's only one option: Force the TOC to be always expanded and preventing unregistered users from collapsing it.
The code forces the TOC body to be visible, and hides the collapsible link (since it will be rendered useless).
This code affects only unregistered users because the CSS class "TOC_hide" is appended to the body only for them, and when that wikia feature is active.