Woo! Way to go! :D I guess I don't have to tell you that clearing Arena is quite tough in Nightmare!, what with monsters from previous rounds respawning, so this is quite an accomplishment! :) It looks like you've discovered, as I have, that Hellrunner is a big asset on that level, since it helps in maneuvering your enemies into corpse-stacking positions. And thanks for the credit too! I'm glad my videos helped somebody! :D :D :D
And yeah, in Chained Court Plus, everyone has to be dead at the same time for the wall to disappear which makes it pretty tough, since it's full of tiny enemies. :| To be honest, I don't have a consistent strategy for that level and always find myself improvising, because the Barons start in awkward positions for body disposal. Once they're out of the way, though, it's just a matter of luring all the former humans/captains into the doorways. (or knocking them into the lava if that's more convenient) Best of luck accomplishing that major hurdle next! :)