It looks like you're new here. If you want to get involved, click one of these buttons!
Scavenging information from all over the place. It sounds like Guild Wars 2 April fools event is going to be lots of fun.
The above video is the chip tune music you will be greeted to when logging into the character selection screen on 1st of April.
So far, we know that a new box has appeared in Rata Sum (thanks to Alunae)
There's also this coin I found in game, which links the Super Adventure Box to what we see in Rata Sum
And a new tab has appeared under hero achievements for Super Adventure Box.
It mentions babbles, which we've seen in this thread.
We also know this is likely a jump puzzle, or at least made by our favorite designer (brownie points), /user/Ragged_Scrybe. Why?
"...a game within a game". The coins seem to hint at this!
There are also weapons that seem to be associated with this. (thanks Grinds)
http://imgur.com/a/E0sAb (The shield says Super Adventure Box)
And, overall, it seems to be pointing to an 8-bit, game within a game theme.
Personally, I'm excited as can be. I can't wait to tear into this!
Looks like it's going to be Mario/NES themed with a huge jumping puzzle with pixel weapon rewards such as this.