Assassin's Creed: Brotherhood's Rome multiplayer level will be cloaked in darkness when a nighttime variant is unlocked as soon as the collective player base reaches 25 million kills (
Progress toward the unlock is being tracked on Ubisoft's Assassin's Network under the "Events" tab. While Ubisoft Germany claims that tracking has already begun, the count currently appears to be hidden -- as of publishing, the counter reads a single donut (pictured). That's okay though! It's only more incentive to hop back into AC: B's addictive multiplayer and sneak-stab some fools.
Update: Ubisoft confirmed that the 25 million number is across both Xbox 360 and PlayStation 3 platforms.