Best Ending: Before facing Graham, make sure to collect the Flame Demon, Succubus, and Giant Bat souls from Castlevania: Aria of Sorrow. After defeating him, you can pass through the black mist door and battle two more bosses. If you defeat both, you will unlock "Sound Mode" and "Boss Rush Mode."
Good Ending: Prior to confronting Graham, gather the Flame Demon, Succubus, and Giant Bat souls. After his defeat, you can proceed through the black mist door and face two additional bosses. If you defeat the first but lose to the second, you will unlock "Boss Rush Mode."
Bad Ending: Defeat Graham, but do not collect the Flame Demon, Succubus, and Giant Bat souls.
Worst Ending: Lose against Chaos.