The mist well gives mist only if ye stock in amount of CE (some has minimum least to stock in, e.g. minimum energy needed to put is 500 ce) and transmute into mist. It also gives another 20% of mist transmuted from the amount of CE put into mist well.
Only works for guildsmens. Public usage is not allowed.
There are so many threads about this...
http://forums.spiralknights.com/en/node/68463
http://forums.spiralknights.com/en/node/68435
http://forums.spiralknights.com/en/node/68443
...and that's not even counting the thread at the top of General Discussion, where the main discussion of everything related to the update is happening. Maybe try there, if you're not satisfied here.