I've noticed that the [spoiler][/spoiler] or [hide][/hide] bbcode is not supported on this forum. It can be very useful when you want to add lot of pictures or lengthy text to your post without making everyone to scroll past them for an hour every time. If you want to read what's under the spoiler, you just click it and it expands
It usually looks like this:
Found couple implementations here and here, looks like it should be easy to add this feature. Of course I don't know anything about phpbb, so may be wrong here
P.S. I've also tried to use youtube tag couple time, not sure if it's working, It should embed video on the page, right?