*Edit: I guess forum won't allow me to embed youtube video here so I'm just add a link to it.
I'm quite sure you all already aware easy exploit from Iron gate 19-20 floors.
This video is for those who don't know it yet.
Iron gate 19th floor is a deconstruction zone which has the shortest entrance-exit distance of all map type.
So what you do is you just run to the exit at 19th floor to see if u r getting "Treasure Vault" at 20th floor.
If u get it, great! If u don't, u just go back to 18th and try again.
It might be better to do it alone due to the fact that ur party member might take a long time to load.
I had some luck while recording this and had earned about 200ish fire crystals just under 1 hour.
This gate will be closed in 3 days so GL to every1 who tries this :)
http://forums.spiralknights.com/en/node/86857