I got the key for the very last boss so I decided to go back and get all the Marks that I missed. The trouble is the game does not tell you what areas still hve collectibles in them and the teleport doesn't take you to every level. So you are basically forced to go through entire levels again. I've now got all the Marks but now I have to backtrack through a couple more levels to get to a teleport. I know it's not really a huge deal and it is still a great game but I'm just blowing off some steam here cos i found it quite annoying.

I was really glad that getting the Marks revealed the treasure chests on the map, but it was a little bit annoying to have to go to each screen with no teleporter in order to see if there were any Marks there that I had missed. Took me a few extra hours after beating the game to get everything but managed to do it okay without a FAQ.

Getting collectibles in most games is the biggest pain in the arse ever.

I guess its half the fun...