Talk:Summoners' Research Lab/@comment-25867638-20150313140231/@comment-24.78.111.81-20150313211534

You need to farm for units that has a chance to level your unit's BB when you fuse them into it. Those are called "BB fodders", they have a flashing "BB?!" on them when you're trying to fuse them.

You can farm fodders for offensive BBs in Mistral > Monster's Nest > Manipulator of the dark.