MB360 (which stands for Mega Blocks 360) is a planned building project at 1200 4th St. in Mission Bay.
The project will have over 300 hundred apartments in two buildings. One of the buildings burned down in the March 11, 2014 Mission Bay Fire - a 5-alarm fire that could be seen from many parts of the city.
However, the project is moving forward and construction on the destroyed building is set to start up again in spring/summer 2014. CurbedSF reported on April 9, 2014: "The destroyed building will have 172 units and is now expected to open sometime in mid-2016. The other half of the complex, with 188 apartments, was relatively undamaged and is expected to open this fall. The complex's original developer, BRE Properties, has been purchased by Essex Property Trust since the fire, and it is Essex that will take the project forward." Here's another article about the future of the project (this one from April 8, 2014).
All of CurbedSF's reporting on this project can be found here.