So in the first 24 hours I was able to get 25 million. The thing about this prize fight is that you kind of have to adjust your playstyle a bit. Once you get used to it, it's not that bad. I guess I'll throw in some tips:
1.
RANGED Unblockable charge attacks are going to be your best friend
Ranged unblockable charge attacks provide lot of damage while only hitting once, which causes BB3s to fill up minimally. By "ranged," I mean charge attacks that allow you to hit from a distance such as Filia's, Cerebella's, Painwheel's, and Big Band's. If you can corner an enemy right off the bat and have the spacing between you and the AI such that the AI is just at the edge of your charge attack's range, you can relatively safely just spam unblockable charge attacks and the AI will usually be KO'd before their BB3 charges. Be cautious of enemy tag outs and BB1/BB2s.
2.
If your character has the ability to almost 1-combo-KO a character, first drop combos before doing a full combo
If your character has the ability to take away 75% with a full combo, start off the fight by only doing part of the combo (ie. do the first part of a combo but don't jump attack after a launcher). This is because when you only do a partial combo you are doing enough damage to get the opponent into KO range for your full combo while also not hitting enough for the AI's BB3s to charge up. To put things into perspective, say you start off the fight by doing the first part of a combo before dropping and it only takes away 30% of their health, their BB3 would only be about 50%-75% charged, so when you punish their next attack with a full combo that would take away 75% of their health, you would have successfully KO'd a fighter before they could activate a BB3. As opposed to doing a full combo off the bat and charging their BB3 to full due to the extra hits from a full combo, leaving you vulnerable to a wake up BB3.
3.
No Egrets Parasoul, Bad Ms Frosty FIlia, Big Top Cerebella and Last Hope Valentine are the most useful fighters for this prize fight
No Egrets Parasoul and Bad Ms Frosty Filia have a chance to disable Blockbusters on hit for a few seconds, making you less likely to get hit with a BB3. Big Top Cerebella and Last Hope Valentine have the ability to resurrect themselves after they have been KO'd, this makes them invaluable BB3 fodder in case the AI is able to charged a BB3. If you plan to use no Egrets Parasoul, Bad Ms Frosty Filia, or Big Top Cerebella, I recommend you evolve them to gold, as they may struggle to survive in high level gold fights otherwise.
4.
Only choose to fight AI generated teams
As tempting as it might be to fight player teams, if you want to keep your streak alive, choose to fight AI generated teams (ie. Aeon and Venus). AI generated teams don't always have BB3s equipped to each character, so that removes the headache entirely. Also, if the AI generated team does have a BB3, there's a 2/3 chance that the BB3 will only be silver or bronze, so your chances of surviving said BB3 improve drastically.
5.
Try equipping 1-hit specials
1-hit specials, such as George's Day Out and Brass Knuckles, do absurd amounts of damage while also charging the opponent's BB3s minimally.