Hopefully penguins ship respawns and that counts. I know on top of gcpd building does

Positive. I got 100% of them using Silent Takedowns and nothing else. The first time, I finished off the last guy with a gliding kick and I noticed that it failed to give me any reward including the achievement. When I did it using only Silent Takedowns, it gave me Silent Knight but not the one that you need to complete Nightmare or whatever it is.

I think you can only get one acheivement per preditor room. I remember doing one with the first group I. A room and noticing I coukd atill complete the next challange with whats left but only one per room unfortunately

Had a multiplayer idea which I thought id add to that.You can choosebto play as batman robin nightwing or any one of many assasins or villians with their own unique abilities. Then everyone is thrown in to a big map the size of a district and you have to take each other out. Last man standing wins

That's def a bug, AD. Happened to me, too. I ended up getting it later during a precinct thing. Also couldn't get the first one on the one where you have to do a grapple takedown on a ledge at first or the sonic batarang one, either.

I love this game but I haven't touched it in a long time. I haven't beaten it yet either which is pretty bad because I don't really remember what happened when I last played it.