Dude, I'll give you a detailed strategy for beating Bass BX.
Navi Customizer: Compressed Undershirt (Code: RRALLRAABB); Compressed NumberOpener (Code: AAALAABLRA)
Regular Chip: Reflector3 * (S-rank against RareMettaur2 in CentralArea1)
Tag Chip: AreaGrab * and DoublePoint *
Other Must-have chips: MachineGun3 (any code); Attack+30 *; SuperVulcan V
Turn1: Chips (in this order): AreaGrab *; MachineGun3; Reflector3 *
First, use AreaGrab when he is not in the front panels. You'll have to take some damage from his machine gun. Next, when he moves to the back row to use his ring attack, counter it before the rings are launched and enter full synchro. When he moves to the front row to use his Gospel Breath, counter it by getting right in front of him and using the Reflector3. Go back to the custom screen.
Turn2: Chips (in this order): DoublePoint *; SuperVulcan V; Attack+30 *; You will also have to Beast Out.
Back up one panel and use DoublePoint IMMEDIATELY. Next, QUICKLY fire the SuperVulcan. With its 10 hits and all the powerups from DoublePoint, Attack+30, BeastOut, and Full Synchro, it will deal a total of 2800 DAMAGE!!!!! And that's that!
After beating him, you'll get HubBatch J. Also, afterward you will randomly encounter FBeast SP in Underground1, and Bass BX in the Graveyard.
One more reward: you can fight RV navis in the Graveyard by examining glowing graves. Your reward is 3000 zennys per defeated RV navi.