To make your spoiler working, you can do this:
First, you should use Source editor

This will add the button:
<div class="mw-customtoggle-Spoiler wikia-menu-button">- - - - Show / Hide Spoilers - - - -</div>

This will make actual collapsed spoiler:

<div class="mw-collapsible mw-collapsed" id="mw-customcollapsible-Spoiler">
A spoiler

If you want to make multiple collapsed spoilers you sould use different id in spoiler div's. Else action on one will lead to action on all spoilers with the same id.

Just in case, I'll leave that here:

- - - - Show / Hide Spoilers - - - -

A spoiler

Deeper spoiler

Another spoiler

One more spoiler

I found this information in Source editor after someone fixed my spoilers in Dosey's page.
Exuse me, I forgot who was it ._. . In case you see it - thank you! And show yourself for personal thanks! =)
Those pesky spoilers do not work in preview mode. Care!

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