IAmA - I am the sysadmin who moved your forum. AMA!

[Shadowfang]

[video]https://www.youtube.com/watch?v=0CFuCYNx-1g[/video]

I can't get it to work. I could just go to the white when I need to, but if there is a code for it, then I'd be interested in learning it

I suggest you stick with the default theme if you want to embed videos. MyBB doesn't use these codes the same way as phpBB3.
In MyBB you get the default editor which generates the codes for you. If you add any code manually, it will convert the "[" and "]" characters so that they show up.

Compare undeadline[u] with [u]undeadline
[/u][/u]