Plugins are great for doing small things but if you are looking to do some more complex stuff then many plugins can cause insatiability of the forum script, slowness, increase server load, and many will even create security issues so if you need to use plugins I recommend to use only very simple plugins that will not cause any of the problems I have described above.
Now let me show you how you can turn MYBB simple quick reply form into an advanced one, basically we will use a form from the newthread and editpost templates in our quick reply form
There are a few plugins that can do that but I have found them to interfere with other MYBB functions so don't use them!
Advanced Quick Reply Form
AJAX QuickReply
This will require core edit but don't wary it's a simple copy and paste process.
In showthread.php find
Above it add this code
$codebuttons = build_mycode_inserter();
The final code should look like this
Now in ACP>>Templates & Style>>Templates>>YOUR TEMPLATE>>Show Thread Templates>>showthread_quickreply find
<textarea style="width: 100%; padding: 4px; margin: 0;" rows="8" cols="80" name="message" id="message" tabindex="1"></textarea>
Add {$codebuttons} the final code should look like this
<textarea style="width: 100%; padding: 4px; margin: 0;" rows="8" cols="80" name="message" id="message" tabindex="1"></textarea>
{$codebuttons}
That is it you are all set, if you have any feather questions feel free to post them here.