Metroid Prime: Blast Ball was first revealed during the Nintendo World Championships 2015, before Metroid Prime: Federation Force was even announced. It’s one of the modes from MP Federation Force, but it was released as a stand-alone free game (“demo” in North America) on the Nintendo eShop a few weeks earlier.
Unfortunately, if you want to keep on playing online, you will soon have no other choice but to buy Metroid Prime: Federation Force. A notice on the Nintendo eShop indicates that online play for the stand-alone/free version of Metroid Prime: Blast Ball will go offline after December 31st:
Thank you for your continued support. The online multiplayer feature for the Metroid Prime: Federation Force Blast Ball demo will be discontinued at 2016/12/31 23:59 PST. The discontinuation of this demo feature will not impact the online multiplayer feature available in the full version of the game.
The good news is that local multiplayer will keep on working after December 31st, so if you don’t care about online multiplayer, you will not have to delete Metroid Prime: Blast Ball. Also, it’s not clear whether the game/demo will be pulled from the Nintendo eShop altogether, but there’s nothing that indicates it will (we will make sure to update this post in case Nintendo does end up pulling Metroid Prime: Blast Ball from the Nintendo eShop).
Naturally, online multiplayer for Metroid Prime: Blast Ball within Metroid Prime: Federation Force will not be impacted.
Source: Nintendo eShop
Thanks Regiruler for the heads up!