The fourth dungeon designed based on player surveys. You can pick up the essential Naga and masks for evolving fire-type monsters, including Divine Carmine Mask.
A quick warning... while this is by far the best way to get a naga, this dungeon is soul-crushing. It's not really hard, but the drop rate for nagas is very low, somewhere around 15% on Expert and somewhere around "haha, you're not serious" on Novice/Intermediate. If you're going for a max-skill Echidna - and every PAD player will, eventually, because she's awesome - expect to run this dungeon a lot and take full advantage of x2 drop days.
With normal naga drops and x2 skill up chances, it will take somewhere in the neighborhood of 160-170 Expert runs to max skill a naga. This goes down to a more reasonable 83 when Nagas are on double drop. Your own experiences can and will vary wildly!
December 13-15, 2013
December 27, 2013
February 22-23, 2014
May 19-20, 2014
Crimson Lotus Mistress, Echidna
With an extremely useful enemy-delay skill, as well as providing much-needed RCV for fire types, Echidna is a must-have for many different teams. Also invaluable in dungeons where the boss needs to be swept. Her ultimate form works almost as well as Fire Serpent God, Hino Kagutsuchi as a lazy-farming leader.