wikiamonobook.user.js

// ==UserScript==
// @name        Wikia Monobook
// @include     *.wikia.com/*
// @grant   none
// ==/UserScript==

(function() {
    var loc = window.location.toString();
    if(loc.indexOf('useskin=monobook') === -1){
        location.replace(loc + (loc.indexOf('?') === -1 ? '?useskin=monobook' : '&useskin=monobook'  ) );
    }

    var a = document.getElementsByTagName('a');

    for (var i = 0; i < a.length; ++i){
        if(a[i].href.indexOf('wikia.com') === -1){
            continue;
        }
        a[i].href = a[i].href + (a[i].href.indexOf('?') === -1 ? '?useskin=monobook' : '&useskin=monobook');
    }
})();