There area some changes and additional things here in BF2 compared to BF1. Specifically, in this guide, with farming BB levels. In BF1, you can fuse a unit with a random success (except burst frogs) but 1 unit is equivalent to 1 BB lvl. When fusing burst frog and burst emperor, you can instantly increase BB lvls by 1 and 5 respectively. Here in BF2, BB lvls now have BB exp increasing as the BB lvl goes higher (as usual). You can still fuse units but now 1 same unit = instant 10 BB exp, while other units = 1 BB exp at random success. Burst frogs are now changed to burst cookies which have an instant 100 BB exp each. The downside is each unit fused costs zel increasing as the lvl goes higher, especially for now that gaining zel is kinda slow. Here in BF2, your units can now gain EXP including BB EXP while doing quests. Each BB activated is equivalent to 1 BB exp exclusive to the unit who cast it. We can utilize this method by activating BB's as many as we can in 1 quest to be effective. I have made a YouTube video for visual guides in here >>> Brave Frontier 2 Farming BB Guide Without Gem. Since our aim is to cast BB many times, we need a quest with many enemies and battles. In the video, I introduced the quest Breaking Through In Enemy in Grand Gaia > Empire of Bariura > Ignorance Steep Path because it has a total of 13 or 14 enemies for 3 battles. To prolong the fight, you can select a specific enemy to kill only 1 enemy every turn. That will make it a total of 13 or 14 turns per run. Since some of the BBs only deals damage to a single enemy, this is very effective. For units who deal damage to several enemies, like enemies in 1 row, make sure to cast the BB to a row of only 1 enemy. If there are 2 or more enemies in each row, you can just do normal attack. To make sure there will be only 1 enemy in a row when your BB gauge is full, you can kill an enemy in a row of more than 1 enemy while doing normal attacks or casting BB to a single enemy until only 1 will be left. Now, another issue is filling the BB gauge. BB fill rate in BF2 is kinda slow without proper buffs and leader skills. In the video, I used Lilith because her LS is very effective for BC drop rates during spark. Of course, you can use other BB type leader skills like increasing BB fill rate or effectiveness, and the like. Equipping spheres is also necessary to fill BB gauges faster. Of course, if you have extra pennies or you're very rich, you can just buy gems and exchange it to burst cookies to max out your BBs faster. If you're hardworking enough to love this game, this may suit you. I hope you find this helpful. Good luck.