Well, we played it yesterday with me as OL, and while i stomped the players in act 2, the final was very close. Had they not missed 3 out of 5 attacks they had won (just one attack more had to hit).
What they did was ignoring the two iron thinges close to where they started (where changelings and zombies spawn) and then rushed to the next one, stopped the creatures (that started there) and then made their stand there.
Just note that you can see the last iron lock from where the prison bars is, so you will have to keep an eye out for any ranged creatures trying to back door that way.
I sen Mirklace in to shoot from that bar, with his plot deck card giving him 1 ekstra attack for 4 damage he should bring it down, i had rylain as a backup with influence. Mirklace had at this stage 5 hp left, so in the end he died when he destroyed the lock. Between volucrix reavers and the plot card that allows them to attack through each other i managed to bring down the lock where the open group starten, but it was sooo close.