That mini game server will be broadcast in August with ドライトのゲーム実況ちゃんねるン interactive live stream!
Build Battle is a competition between 2 or more players. Players are given a theme, either chosen randomly, choosing a theme, or voted. After the timer starts, players has to build something related to the theme. After the timer stops, the players look at others' builds, and voting using items in their hot bar. You cannot vote for yourself though. The best voted build wins.
Play screen (this is an old photo)