Bloodstained Ritual of the Night has a lot of secrets. By 'a lot' we mean 'a metric ton', too, and they range from goofy easter-eggs and cheats all the way to huge bosses, weaponry, and other awesome stuff. A particular boss can be found behind a locked door, and to open it, you're going to need the Millionaire Key.
The Bloodstained Millionaire Key is pretty well-hidden, and will require some perspective-flipping to reach. The boss is, aptly enough, named Millionaire's Bane, and it's going to be a pretty challenging fight. Learn how to access it down below!
Where is the Millionaire Key in Bloodstained?
Firstly, to even reach the chest with Millionaire Key, you're going to need to use Miriam's Invert ability, which will allow you to manipulate gravity and walk across the ceiling. The chest itself can be found in Den of Behemoths, in the upper left corner of the room. It will take a bit of trial & error before you can get to it, but the location itself is the most taxing issue, really.
When you have the key, you're going to want to make your way over to the Hall of Termination, where finding the door that the Millionaire Key opens shouldn't be more problematic. On the other side, you'll find the Millionaire's Bane creature, which is essentially a mimic, and has 12% chance to drop the Jackpot Shard.
Of course, there are ways about making all of this somewhat easier. Cheats, for example, might give you the edge you need to either reach the Millionaire Key or help you take down the boss itself, but if you're not into that, the upcoming COOP mode might be more your speed.