You will have noticed by now that a new editor has been implemented.
Since the smilies do not work with the editor it has been removed from the sidebar. You can, however, still add smilies to your posts using the smilie icon in the editor.
Previous myBB codes are still available in the new editor.
You will also note that it is now possible to copy and paste from other websites into your posts. Making it much easier to introduce the contents of another site. Please be sure you do not breech any copyright laws by doing so. Also name your original source.
Be aware that copying from other sites will intoduce a lot of 'noise' which only makes sense on the other site. Therefore, though your message looks fine when you compose it, there may be redundat code displaying once you post the message.
There is an icon with a 'Toggle fullscreen mode'. This can be used for large messages. Once you completed the message you simply click on the icon again to bring the contents into your post before you post the message or thread.
Please let us know if you have any issues with the editor.