oh, I see XD

Well, got stuck in the 5.18 now.. really, splitting the field in half removes any strategy element the game may have had and hands your balls to RNG... the boss kills you in 2 hits unless you spend unreasonably much to withstand 3 hits....
The only way to win it is pretty much to BOTH have enough attack to kill him in 2 turns(not too rare with some RNG) AND gather 10 stack of blue(or 5 if you get very lucky with reds, but you probably won't gather ~300 atk with 2 lines) within this time... essentially this requires the same side of field to double buff the blue stack twice AND have enough attack to finish it off..
magnet booster makes it pretty much trivial but the fact that game absolutely demands that you use booster or face unreal odds is pretty shit...