The "Bomb-Up Pack 1" DLC was released for http://www.trueachievements.com/Bomberman-Battlefest-xb....htm
on December 29th, 2010, but the achievement that came with it has only now been added to Xbox.com. Those of you who had unlocked it before now would have noticed that the 10G was not added to your gamerscore.
That is no longer the case; those of you who had held off from trying to unlock the achievement will now be able to play without any worries. Unfortunately, for those of you who had unlocked the achievement beforehand, you will have to recover your gamertag and then earn the achievement again for it to be added to your gamerscore.
Here's a brief description of the DLC if you were unaware of its release:
Craving more Bomberman action? Put on your Power Glove and go low-gravity with the all-new Asteroid arena! Bomb your opponents into traffic in Intersection! Dress up in two new costumes, the mighty Bombzilla and the heroic Firebomb!
The DLC costs 240 MSP and is available for download from here