You defeated the Monsters, but you didn't kill them. Here's a section from the FAQ that you seem to have forgotten to mention:
Quote:
|
Originally Posted by The FAQ
"Killed" means that you defeated the monster with your Level and bonuses in combat, or used some card or special ability that specifically states that it kills the monster. For this, you get levels and Treasure.
|
You also didn't kill the Monsters; thematically, you traded Bad Stuff for a Level, and then the Monster left.
Finally, Since the boon doesn't explicitly say it can be used for the Winning Level, you can't use it at all if you're going to get the Winning Level.