Bloodstained: Ritual of the Night - Bloodbringer Duplication Glitch
This is what works for me. Have Bloodbringer active, and level it until it reaches 25 and changes color. Then use Shortcut to swap to a build with a different familiar, then swap back to the one with Bloodbringer. Your extra Bloodbringer should stay out even if you change familiars, but it will reset if you leave the game, or die, or it just feels like resetting. I'm not sure if having two Bloodbringers out doubles the experience gain for it, but from my very limited testing, it seems... maybe?
https://store.playstation.com/#!/tid=CUSA07953_00
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