In order to battle the Legion, a floating mass of dead bodies you first must obtain the 5th Innocent Devil, the Devil Type. With this, head back to Garibaldi Temple, and slide under the crack in the wall near the area with the four courtyards and Fencers. Travel down these hallways into the basement until you come to an area that seems to be "beating" like a human heart. Avoid the Evil Cores, and enter the boss door.
After you beat Crazy Mode, the Moebius Brooch will be available in the shop. Equip it and it allows Trevor to use sub-weapons without using hearts.
To get to the Tower of Evermore, you'll need a bird type Innocent Devil with the long glide ability. From the top of the Tower of Eternity, face the moon in the background so that it is directly in front of you and jump off the ledge, gliding all the way to the Tower of Evermore.
The monsters here are much harder than the ones found in the Tower of Eternity.
Simply sit in the 23 other chairs in the game. Don't forget about Dracula's Throne during the final fight with him; it's your only chance to sit in it.