I was thinking that Monica seems a bit underpowered, but then I realized Monica is the only person who seems to be able to kill easilly. Sure, Prudence can burn people, and Oda has that Scythe, but all Monica really needs to do is stab a ghost or a vampire in the heart or the head, and they'll go down like any mortal. Of course, she has to get within stabbing range, and obviously it's less effective against stronger types, but the idea is there.