Thanks for the reply.
Bloodfly was a joke. :) You just can never get rid of it. Even when it finally goes back into the box at the end of a scenario, it somehow gets shuffled into the next scenario again and again.
I guess I want to say if you are only using the danger as, "Hay, MAYBE a card that accesses it will come up just to spice things up but odds are it won't..," please just don't put it into that particular scenario. We love the thematic aspect of it and are asking you to use it more. The game takes long enough to setup and put away. We'd rather not have to spend the time building a side deck or even a single card if the odds are that there is only a 25% that we might only encounter it once.
To sum up: If there is a reason for the danger to be there and the players are going to encounter it a few times in a scenario then please include it. If you have a scenario that only has a danger in it with little chance of it being encountered even once no less a few times then just don't put it in there.
We have not read the CotCT rule book so we did not know we don't have mix all the boons together in the expansion. We are glad to hear it was a core box mechanic only!!