There are three ways I can think of to do it:
A) Have ten switches called ghost1, ghost2, ghost3, etc. Whenever you beat a ghost it turns on a switch. When all ten switches are on you can go back to the guy who gave you the quest or whatever, and then you have a conditional branch do something to check it. This is a stupid way because it takes ten switches and is too long and complicated.
B) Have each ghost drop an item like "Sheet" or "Ectoplasm" (Ghostbusters, anyone?
![Grin ;D](https://rmrk.net/Smileys/default/grin.gif)
), and then put a conditional branch in your quest-giver that says you have ten sheets or something. But personally I recommend:
C)Whenever you kill a ghost, it adds one to a variable called ghostQuest or ghostKill or something like that. The quest giver has an event page that requires the variable ghostQuest is equal to or greater than 10. In that page you can make him say "Congratulations, take an apple pie" or whatever you want.
The reason you should do it like C is because you don't have to set up any extra items, you don't waste switches, and you don't even need a conditional branch.
If you don't know how to adjust variables when a ghost dies, or how to make an event page require that a variable be equal to or greater than something, just ask.
~Arkhan