This is a new and improved version of my Spoiler MyCode available on the old mods site. This has been updated to work with MyBB 1.8.x and contains a fresh new look to go along with the new look of MyBB.

To install; upload the single file to /inc/plugins and activate it in your AdminCP.

Then, for each of the themes you have installed, you need to add in some new CSS. This CSS is based off of the MyBB Default theme for 1.8

.spoiler_wrap {
    margin: 4px 0;
}

.spoiler_header {
    background: #0f0f0f url(images/tcat.png) repeat-x;
    color: #fff;
    border-top: 1px solid #444;
    border-bottom: 1px solid #000;
    padding: 0;
    font-size: 12px;
}

.spoiler_body {
    background: FFF;
    padding: 4px;
    border: 1px solid #CCC;
    border-top: 0;
    color: #000;
}

.spoiler_header .expandspoiler {
    float: right;
    cursor: pointer;
    margin-top: 2px;
    margin-right: 3px;
}

.spoiler_header a:link, .spoiler_header a:visited {
    display: block;
    padding: 6px;
    text-decoration: none;
    color: #FFF;
}