Board Thread:Support Requests - Designing Your Wiki/@comment-44457912-20200814002645/@comment-43689784-20200814020034

Two of them use SpoilerAlert, and one of them uses SpoilerBlur (which you mentioned). Since you don't have MediaWiki:ImportJS, create a page called MediaWiki:Wikia.css. Once that is created, paste either @import url("/load.php?mode=articles&articles=u:dev:MediaWiki:SpoilerBlur/code.css&only=styles"); or request for MediaWiki:ImportJS to be added. Once MediaWiki:ImportJS is added, paste dev:SpoilerAlert/code.js. If you need help, just ask.