When using the lamp with them reunited, fire in a direction and Charon (blue beard guy) will move in that direction. He's like a familiar that you control via your space at item.

As for the Tomb, you need to beat Glacier and a door will pop up that leads to the Tomb. Apparently, you can also access the Tomb in Caves shops.

Basically Dante starts in one part of the level, and Charon in other, and you have to get them together to be able to open the boss door. Once they reunite, you can use the lamp to direct where Charon shoots while you control Dante. A bit complicated, but practice makes perfect, or so they say

Has anyone else had the experience of Charon just not shooting anymore once they are reunited? He became dead weight for me, I just couldn't shoot in the direction he was facing at all.

引用自 maxastro：

Has anyone else had the experience of Charon just not shooting anymore once they are reunited? He became dead weight for me, I just couldn't shoot in the direction he was facing at all.

I'm getting that too. I'm just playing this for the first time so maybe I'm doing something wrong? It seems like a glitch to me.

Whenever I Get A Usable When Charon And Dante Are Reuinited, Charon Just Fires In One Direction.. Weird

After each cleared room you must swap to the other, by using your active. The goal is to unite them. When you pick up an item, and zelda it over your head, you have a window to use your active item, and send it to the other character. When your characters are merged, you can press your active, and then a direction to change the direction Charon is firing.

Charon gains increased damage and knockback the longer he fires in one direction.
Dante can smack enemies with his book to apply a large damage debuff on enemies for a short time.