1. Create two characters.
2. Optional - defeat the unspeakable depth with at least one (the other way is farming salt enough to lvl up)
3. Leave both characters in the altar of a sanctuary (it doesn't have to be the same sanctuary, but it has to be one available/unlocked)
4. Select one character, go to the exit menu, enlighten ''Yes'', and then press fast X O X and hold SQUARE for 5-10 seconds, you will hear the sound of the leveling menu if you did it right, press X and then press continue.
5. Select the other character, the character will level up as many times the other character would have level up, but will gain negative souls, just die twice to get rid of it. Note: Max level is 549, going upmore than that level will just crash the game.