Culex- culex is in the dark knight of vanda quest area, Once completing the quest with the vampire tokens you can kill culex every 20 minutes or so. If your team dies to culex, remember it still takes 20 minutes until you can pull the lever again. Culex main item drop that people look for is the EXP FISH! WHich is a great way to earn double exp for 1 hour.
Killing Culex you are required to kill some orbs before you kill culex. Main goal is to focus the Fire orb first, Then the wind orb second. If your knight has enough HP you can now attack Culex, If you are worried about dieng still Kill the other orbs to make it easier to finish off culex.